Filed Pursuant to Rule 424(b)(3)
Registration No. 333-130549

SUBJECT TO COMPLETION, DATED JANUARY 5, 2006

PRELIMINARY PROSPECTUS SUPPLEMENT

(To Prospectus dated December 21, 2005)

                            Shares

NRG Energy, Inc.

Common Stock

We are offering                                shares of our common stock. The closing of this offering is not conditioned on the consummation of our acquisition of Texas Genco LLC described elsewhere in this prospectus supplement. Concurrently with this offering, we are offering senior notes and shares of our mandatory convertible preferred stock. This offering is not conditioned on the consummation of these concurrent offerings.

Our common stock is listed on The New York Stock Exchange under the symbol “NRG.” The last reported sale price of our common stock on The New York Stock Exchange on January 3, 2006, was $47.95 per share.

Investing in our common stock involves risks. See “Risk Factors” on page S-12 of this prospectus supplement.

The underwriters may also purchase up to an additional                               shares from us at the public offering price, less the underwriting discount, within 30 days from the date of this prospectus supplement to cover any overallotments. If the overallotment option is exercised in full, we will receive additional proceeds, before expenses, of $                    .

Neither the Securities and Exchange Commission nor any state securities commission has approved or disapproved of these securities or determined if this prospectus supplement or the prospectus to which it relates is truthful or complete. Any representation to the contrary is a criminal offense.

The shares will be taken for delivery on or about                     , 2006.

Joint Book-Running Managers

LEHMAN BROTHERS

The date of this prospectus supplement is                     , 2006.

TABLE OF CONTENTS

Prospectus Supplement

Prospectus

About This Prospectus Supplement

      This document consists of two parts. The first part is this prospectus supplement, which describes the specific terms of this offering. The second part is the accompanying prospectus, which describes more general information, some of which may not apply to this offering. You should read both this prospectus supplement and the accompanying prospectus, together with additional information described below under the headings “Where You Can Find More Information” and “Incorporation of Certain Documents by Reference.”

      If the description of the offering varies between this prospectus supplement and the accompanying prospectus, you should rely on the information in this prospectus supplement.

      Any statement made in this prospectus supplement or in a document incorporated or deemed to be incorporated by reference in this prospectus supplement will be deemed to be modified or superseded for purposes of this prospectus supplement to the extent that a statement contained in this prospectus supplement or in any other subsequently filed document that is also incorporated or deemed to be incorporated by reference in this prospectus supplement modifies or supersedes that statement. Any statement so modified or superseded will not be deemed, except as so modified or superseded, to constitute a part of this prospectus supplement. See “Incorporation of Certain Documents By Reference.”

Where You Can Find More Information

      NRG files annual, quarterly and special reports, proxy statements and other information with the Securities and Exchange Commission, or the SEC. You can inspect and copy these reports, proxy statements and other information at the Public Reference Room of the SEC, 100 F Street, N.E., Washington, D.C. 20549. Please call the SEC at 1-800-SEC-0330 for further information on the operation of the public reference room. NRG’s SEC filings will also be available to you on the SEC’s website at http://www.sec.gov and through the New York Stock Exchange, 20 Broad Street, New York, NY 10005, on which NRG’s common stock is listed.

      This prospectus supplement and the accompanying prospectus, which forms a part of the registration statement, do not contain all the information that is included in the registration statement. You will find additional information about us in the registration statement. Any statements made in this prospectus supplement or the accompanying prospectus concerning the provisions of legal documents are not necessarily complete and you should read the documents that are filed as exhibits to the registration statement or otherwise filed with the SEC for a more complete understanding of the document or matter.

Incorporation of Certain Documents by Reference

      The SEC allows the “incorporation by reference” of the information filed by NRG with the SEC into this prospectus supplement, which means that important information can be disclosed to you by referring you to those documents and those documents will be considered part of this prospectus supplement. Information that NRG files later with the SEC will automatically update and supersede the previously filed information. The documents listed below and any future filings NRG makes with the SEC under Sections 13(a), 13(c), 14 or 15(d) of the Securities Exchange Act of 1934, as amended, or the Exchange Act, are incorporated by reference herein, after the date of this prospectus supplement but before the end of any offering made under this prospectus supplement:

      If you make a request for such information in writing or by telephone, NRG will provide you, without charge, a copy of any or all of the information incorporated by reference in this prospectus. Any such request should be directed to:

NRG Energy, Inc.

211 Carnegie Center

Princeton, New Jersey 08540

(609) 524-4500

Attention: General Counsel

      You should rely only on the information contained in this prospectus supplement, the attached prospectus, the documents incorporated by reference and any written communication from us or the underwriters specifying the final terms of the offering. NRG has not, and the underwriters have not, authorized any other person to provide you with different information. If anyone provides you with different or inconsistent information, you should not rely on it. NRG is not, and the underwriters are not, making an offer to sell these securities in any jurisdiction where the offer or sale is not permitted. You should assume that the information appearing in this prospectus supplement is accurate as of the date on the front cover of this prospectus supplement only. NRG’s business, financial condition, results of operations and prospects may have changed since that date.

Disclosure Regarding Forward-Looking Statements

      This prospectus supplement contains, and the documents incorporated by reference herein may contain, forward-looking statements within the meaning of Section 27A of the Securities Act of 1933 and Section 21E of the Securities Exchange Act of 1934. Such forward-looking statements are subject to certain risks, uncertainties and assumptions that include, but are not limited to, expected earnings and cash flows, future growth and financial performance and the expected benefits and other benefits of the acquisition of Texas Genco LLC described herein and typically can be identified by the use of words such as “will,” “expect,” “estimate,” “anticipate,” “forecast,” “plan,” “believe” and similar terms. Although we believe that our expectations are reasonable, we can give no assurance that these expectations will prove to have been correct, and actual results may vary materially. Factors that could cause actual results to differ materially from those contemplated above include, among others:

Market and Industry Data

      Certain market and industry data included or incorporated by reference in this prospectus supplement and in the accompanying prospectus has been obtained from third party sources that we believe to be reliable. We have not independently verified such third party information and cannot assure you of its accuracy or completeness. While we are not aware of any misstatements regarding any market, industry or similar data presented herein, such data involves risks and uncertainties and is subject to change based on various factors, including those discussed under the headings “Disclosure Regarding Forward-Looking Statements” and “Risk Factors” in this prospectus supplement.

SUMMARY

      This summary may not contain all the information that may be important to you. You should read this entire prospectus supplement, the accompanying prospectus and those documents incorporated by reference into this prospectus supplement and the accompanying prospectus, including the risk factors and the financial data and related notes, before making an investment decision.

      In this prospectus supplement, unless otherwise indicated herein or the context otherwise indicates:

Our Business

      We are a leading wholesale power generation company with a significant presence in many of the major competitive power markets in the United States. We are primarily engaged in the ownership and operation of power generation facilities, purchasing fuel and transportation services to support our power plant operations, and the marketing of energy, capacity and related products in the competitive markets in which we operate. As of September 30, 2005, the combined company would have had a total global portfolio of 235 operating generation units at 62 power generation plants, with an aggregate generation capacity of approximately 25,041 MW. Within the United States, the combined company will have one of the largest and most diversified power generation portfolios with approximately 23,124 MW of generation capacity in 213 generating units at 54 plants as of September 30, 2005. These power generation facilities are primarily located in our core regions in the Electric Reliability Council of Texas, or ERCOT, market (approximately 11,119 MW), and in the Northeast (approximately 7,099 MW), South Central (approximately 2,395 MW) and Western (approximately 1,044 MW) regions of the United States. Our facilities consist primarily of baseload, intermediate and peaking power generation facilities, which we refer to as the merit order, and also include thermal energy

production and energy resource recovery plants. The sale of capacity and power from baseload generation facilities accounts for the majority of our revenues and provides a stable source of cash flow. In addition, our diverse generation portfolio provides us with opportunities to capture additional revenues by selling power into our core regions during periods of peak demand, offering capacity or similar products to retail electric providers and others, and providing ancillary services to support system reliability.

The Texas Genco Acquisition

      On September 30, 2005, NRG entered into an acquisition agreement, or the Acquisition Agreement, with Texas Genco and each of the direct and indirect owners of equity interests in Texas Genco, or the Sellers. Pursuant to the Acquisition Agreement, NRG agreed to purchase all of the outstanding equity interests in Texas Genco for a total pro forma purchase price of approximately $6.121 billion that includes the assumption of approximately $2.7 billion of indebtedness. The purchase price is subject to adjustment, and includes an equity component valued at approximately $2.0 billion based on a price per share of $45.37 of NRG’s common stock issued to the Sellers, and an average price per share of $40.73 for the preferred stock issued to the Sellers. As a result of the Acquisition, Texas Genco will become a wholly-owned subsidiary of NRG. Each of NRG’s and the Sellers’ obligation to consummate the Acquisition is subject to certain customary conditions, including the receipt of required regulatory consents and approvals. See “The Acquisition” for a discussion of the Acquisition.

      The closing of this offering is not conditioned on the consummation of the Acquisition. While we expect that the Acquisition will be consummated in or about the first week of February 2006, no assurance can be given that the Acquisition will be completed in accordance with the anticipated timing or at all. See “Risk Factors— Risks Related to the Offering— There can be no assurance that the Acquisition will be consummated in accordance with the anticipated timing or at all, and the closing of this offering is not conditioned on the consummation of the Acquisition. If the Acquisition is not consummated, NRG’s common stock will not reflect any actual or anticipated interest in Texas Genco, and if the Acquisition is delayed, this interest will not be reflected during the period of delay.”

Our Strategy

      Our strategy is to increase the value of, and extract value from, our generation assets while using that asset base as a platform for enhanced financial performance which can be sustained and expanded upon in years to come. We plan to maintain and enhance our position as a leading wholesale power generation company in the United States in a cost effective and risk mitigating manner in order to serve the bulk power requirements of our customer base and other entities who offer load, or otherwise consume wholesale electricity products and services in bulk. Our strategy includes the following elements:

      Increase value from our existing assets. Following the Acquisition, we believe that we will have a highly diversified portfolio of power generation assets in terms of region, fuel type and dispatch levels. We will continue to focus on extracting value from our portfolio by improving plant performance, reducing costs and harnessing our advantages of scale in the procurement of fuels: a strategy that we have branded “FORNRG,” or Focus on ROIC@NRG.

      Pursue intrinsic growth opportunities at existing sites in our core regions. We believe that we are favorably positioned to pursue growth opportunities through expansion of our existing generating capacity. We intend to invest in our existing assets through plant improvements, repowering and brownfield development to meet anticipated regional requirements for new capacity. We expect that these efforts will provide more efficient energy, lower our delivered cost, expand our electricity production capability and improve our ability to dispatch economically across the merit order.

      Maintain financial strength and flexibility. We remain focused on increasing cash flow and maintaining liquidity and balance sheet strength in order to ensure continued access to capital for growth; enhancing risk-adjusted returns; and providing flexibility in executing our business strategy. We intend to continue our focus on maintaining operational and financial controls designed to ensure that our financial position remains strong.

      Reduce the volatility of our cash flows through asset-based commodity hedging activities. We will continue to execute asset-based risk management, hedging, marketing and trading strategies within well-defined risk and liquidity guidelines in order to manage the value of our physical and contractual assets. Our marketing and hedging philosophy is centered on generating stable returns from our portfolio of power generation assets while preserving the ability to capitalize on strong spot market conditions and to capture the extrinsic value of our portfolio. We believe that we can successfully execute this strategy by leveraging our expertise in marketing power and ancillary services, our knowledge of markets, our flexible financial structure and our diverse portfolio of power generation assets.

      Participate in continued industry consolidation. We will continue to pursue selective acquisitions, joint ventures and divestitures to enhance our asset mix and competitive position in our core regions to meet the fuel and dispatch requirements in these regions. We intend to concentrate on acquisition and joint venture opportunities that present attractive risk-adjusted returns. We will also opportunistically pursue other strategic transactions, including mergers, acquisitions or divestitures during the consolidation of the power generation industry in the United States.

Our Competitive Strengths

      Scale and diversity of assets. The combined company will have one of the largest and most diversified power generation portfolios in the United States with approximately 23,124 MW of generation capacity in 213 generating units at 54 plants as of September 30, 2005. Our power generation assets will be diversified by fuel type, dispatch level and region, which will help mitigate the risks associated with fuel price volatility and market demand cycles. The combined company’s U.S. baseload facilities, which will consist of approximately 8,558 MW of generation capacity measured as of September 30, 2005, will provide the combined company with a significant source of stable cash flow, while the combined company’s intermediate and peaking facilities, with approximately 14,566 MW of generation capacity as of September 30, 2005, will provide the combined company with opportunities to capture the significant upside potential that can arise from time to time during periods of high demand. In addition, approximately 10% of the combined company’s domestic generation facilities will have dual or multiple fuel capability, which will allow most of these plants to dispatch with the lowest cost fuel option.

      Reliability of future cash flows. We have sold forward a significant amount of our expected baseload generation capacity for 2006 and 2007. As of September 30, 2005 the combined company would have sold forward 68% of its baseload generation in the Texas (ERCOT) market for 2006 through 2009. As of the same date, the combined company would have sold approximately 83% of its expected annual baseload generation in the Southeastern Electric Reliability Council/ Entergy, or SERC— Entergy, market for 2006 through 2009, and approximately 70% of its expected annual baseload generation in the Northeast region for 2006. In addition, as of September 30, 2005, the combined company would have purchased forward under fixed price contracts (with contractually-specified price escalators) to provide fuel for approximately 81% of its expected baseload coal generation output from 2006 to 2009.

      Favorable market dynamics for baseload power plants. As of September 30, 2005, approximately 38% of the combined company’s domestic generation capacity would have been fueled by coal or nuclear fuel. In many of the competitive markets where we operate, the price of power typically is set by the marginal costs of natural gas-fired and oil-fired power plants that currently have substantially higher variable costs than our solid fuel baseload power plants. For example, in the ERCOT market, a 2004 report by Henwood Energy Services, Inc., or Henwood, found that natural gas-fired power plants set the market price of power more than 90% of the time. As a result of our lower marginal cost for baseload coal and nuclear generation assets, we expect such assets to generate power nearly 100% of the time they are available.

      Locational advantages. Many of our generation assets are located within densely populated areas that are characterized by significant constraints on the transmission of power from generators outside the region. Consequently, these assets are able to benefit from the higher prices that prevail for energy in these markets during periods of transmission constraints. The combined company will have generation assets located within New York City, southwestern Connecticut, Houston and the Los Angeles and San Diego load basins, all areas

with constraints on the transmission of electricity. This allows us to capture additional revenues through offering capacity to retail electric providers and others, selling power at prevailing market prices during periods of peak demand and providing ancillary services in support of system reliability.

Summary of Risk Factors

      We are subject to a variety of risks related to our competitive position and business strategies. Some of the more significant challenges and risks include those associated with the operation of our power generation plants, volatility in power prices and fuel costs, our leveraged capital structure and extensive governmental regulation. See “Risk Factors” beginning on page S-12 for a discussion of the factors you should consider before investing in our securities.

The Financing Transactions

      The offering of common stock forms part of a larger financing plan for the Acquisition described elsewhere in this prospectus supplement. See “The Acquisition.” Concurrently with this offering, NRG intends to offer, by means of separate prospectus supplements (i) $500 million of its mandatory convertible preferred stock and (ii) $3.6 billion of its senior notes, or the New Senior Notes. See “Description of Capital Stock— Mandatory Convertible Preferred Stock” and “Description of Certain Indebtedness—New Senior Notes.” This offering, the mandatory convertible preferred stock offering and the New Senior Notes offering are expected to be consummated at or prior to the completion of the Acquisition. The closing of this offering will not necessarily be contemporaneous with the closing of the New Senior Notes offering and/or the closing of the mandatory convertible preferred stock offering. The net proceeds of the offering of the New Senior Notes will be placed into an escrow account held by the escrow agent until the consummation of the Acquisition.

      In addition, NRG intends to enter into a new senior secured credit facility at or prior to the closing of the Acquisition that will replace its existing senior secured credit facility. See “Description of Certain Indebtedness— New Senior Secured Credit Facility.” Concurrently with this offering, NRG is conducting a cash tender offer and consent solicitation with respect to (i) all of its outstanding 8% Second Priority Senior Secured Notes due 2013, or the Second Priority Notes, and (ii) all of Texas Genco’s outstanding 6.875% Senior Notes due 2014, or the Unsecured Senior Notes. The completion of the Acquisition is not conditioned on the completion of the tender offer or receipt of the consents for either the Second Priority Notes or Texas Genco’s Unsecured Senior Notes. The completion of the tender offer for the Second Priority Notes and Texas Genco’s Unsecured Senior Notes is conditioned on the completion of the Acquisition. However, NRG can waive this condition in the case of the tender offer and consent solicitation for the Second Priority Notes.

      NRG intends to use initial borrowings under its new senior secured credit facility, together with the net proceeds from this offering, the offerings of mandatory convertible preferred stock and New Senior Notes and cash on hand (i) to finance the Acquisition, (ii) to repurchase NRG’s outstanding Second Priority Notes, (iii) to repurchase Texas Genco’s outstanding Unsecured Senior Notes, (iv) to repay amounts outstanding under NRG’s existing senior secured credit facility and Texas Genco’s existing senior secured credit facility, (v) for ongoing credit needs of the combined company, including replacement of existing letters of credit and (vi) to pay related premiums, fees and expenses. In the event that NRG does not consummate the Acquisition, NRG intends to use the net proceeds from this offering for general corporate purposes. See “Use of Proceeds.”

      The closing of this offering is not contingent on the closing of the mandatory convertible preferred stock offering, the closing of the New Senior Notes offering, the effectiveness of the new senior secured credit facility, the completion of the tender offers and receipt of the consents in connection with the outstanding tender offers for NRG’s and Texas Genco’s notes or the consummation of the Acquisition. See “Risk Factors— Risks Related to the Offering— There can be no assurance that the Acquisition will be consummated in accordance with the anticipated timing or at all, and the closing of this offering is not conditioned on

the consummation of the Acquisition. If the Acquisition is not consummated, NRG’s common stock will not reflect any actual or anticipated interest in Texas Genco, and if the Acquisition is delayed, this interest will not be reflected during the period of delay.” NRG’s obligations under the Acquisition Agreement are not conditioned upon the consummation of any or all of the Financing Transactions.

      NRG has entered into an amended and restated commitment letter, or the commitment letter, with Morgan Stanley Senior Funding, Inc., Citigroup Global Markets Inc., Lehman Commercial Paper Inc., Lehman Brothers Inc., Banc of America Bridge LLC, Deutsche Bank AG Cayman Islands Branch, Merrill Lynch Capital Corporation and Goldman Sachs Credit Partners L.P., or the bridge lenders. Under the commitment letter, the bridge lenders have committed to fund NRG’s new senior secured credit facility and provide, subject to certain conditions, the additional financing required for the Acquisition through a $5.1 billion bridge loan facility in the event that sufficient funds are not raised from this offering, the mandatory convertible preferred stock offering and/or the New Senior Notes offering. See “Description of Certain Indebtedness— Bridge Loan Facility.” In the event that NRG is unable to raise sufficient proceeds through the consummation of this offering, the mandatory convertible preferred stock offering and/or the New Senior Notes offering, NRG may draw down on the bridge loan facility, in whole or in part, in order to finance the Acquisition. In the event that NRG does not consummate the mandatory convertible preferred stock offering and the New Senior Notes offering as currently contemplated and elects not to consummate the financing under the bridge loan facility, it could seek alternative sources of financing for the Acquisition, which may include, among other alternatives, the issuance in part of senior secured debt securities or borrowing in part on a senior secured basis.

Sources and Uses of Funds

      The following table sets forth the expected sources and uses of funds in connection with the Acquisition on a pro forma basis giving effect to the Transactions as if they had occurred on September 30, 2005. No assurances can be given that the information in the following table will not change depending on the nature of our financings and/or whether the Acquisition will be consummated in accordance with the anticipated timing or at all. See “Risk Factors— Risks Related to the Acquisition— Because the historical and pro forma financial information incorporated by reference or included elsewhere in this prospectus supplement may not be representative of our results as a combined company or capital structure after the Acquisition, and NRG’s and Texas Genco’s historical financial information are not comparable to their current financial information, you have limited financial information on which to evaluate us, NRG, Texas Genco and your investment decision,” “Risk Factors— Risks Related to the Offering— If NRG is unable to raise sufficient proceeds through other Financing Transactions described elsewhere in this prospectus supplement, NRG may draw down on a bridge loan facility in order to close the Acquisition which would significantly increase our indebtedness. If NRG elects not to consummate the financing under the bridge loan facility, NRG may seek alternative sources of financing for the Acquisition, the terms of which are unknown to us and could limit our ability to operate our business” and “Risk Factors— Risks Related to the Offering— There can be no assurance that the Acquisition will be consummated in accordance with the anticipated timing or at all, and the closing of this offering is not conditioned on the consummation of the Acquisition. If the Acquisition is not

consummated, NRG’s common stock will not reflect any actual or anticipated interest in Texas Genco, and if the Acquisition is delayed, this interest will not be reflected during the period of delay.”

Recent Developments

      We anticipate that the following transactions will be consummated after the Acquisition and Financing Transactions.

      On December 8, 2005, NRG entered into an asset purchase and sale agreement to sell NRG Audrain Generating LLC, or Audrain, a gas fired 640 MW peaking facility in Vandalia, Missouri to AmerenUE, a subsidiary of Ameren Corporation. The purchase price is $115 million, subject to customary purchase price adjustments, plus the assumption of $240 million of non-recourse capital lease obligations and assignment of a $240 million note receivable. Of the $115 million in cash proceeds, approximately $93 million of the proceeds will be paid to the project lenders with the balance of approximately $22 million paid to NRG. This transaction, which is subject to regulatory approval, is expected to close during the first half of 2006.

      On December 27, 2005, NRG entered into two purchase and sale agreements with Dynegy Inc., or Dynegy, through which the companies will each simultaneously purchase the other’s interest in two jointly held entities that own power generation facilities in the states of California and Illinois, respectively. Under the purchase and sale agreement for the California interests, NRG will acquire Dynegy’s 50% interest in WCP (Generation) Holdings LLC, or WCP Holdings, for a purchase price of $205 million. As a result of this transaction, NRG will become the sole owner of power plants totaling approximately 1,800 MW in southern California. Pursuant to the terms of the purchase and sale agreement for the Illinois interests, NRG will sell to Dynegy its 50% ownership interest in the jointly held entity that owns the Rocky Road power plant, a 330 MW natural gas-fired peaking facility near Chicago, for a purchase price of $45 million. NRG will effectively fund the net purchase price of $160 million with cash held by West Coast Power LLC, or WCP. The transactions, which are conditioned upon each other and subject to regulatory approval, are expected to close in the first quarter of 2006.

      These transactions have been reflected in our pro forma financial statements as filed on our amended Current Report on Form 8-K/A filed on January 5, 2006 and incorporated herein by reference.

      On December 29, 2005, NRG announced that it had received valid tenders and consents from holders of approximately $1,078,137,353 in aggregate principal amount of Second Priority Notes and $1,124,875,000 in aggregate principal amount of Unsecured Senior Notes, representing approximately 99.78% and 99.98% of the outstanding Second Priority Notes and Unsecured Senior Notes, respectively, in connection with the cash tender offer and consent solicitation for the Second Priority Notes and the Unsecured Senior Notes. Consummation of the tenders offers are conditioned upon the satisfaction of certain conditions.

      NRG Energy, Inc. is a Delaware corporation. Our principal executive office is located at 211 Carnegie Center, Princeton, New Jersey 08540, and our telephone number at that address is (609) 524-4500. Our website is located at www.nrgenergy.com. The information on, or linked to, our website is not part of this prospectus supplement.

The Offering

      The total number of shares of common stock to be outstanding as of January 3, 2006 after this offering excludes:

Summary Historical and Pro Forma Financial Information

      The following table presents summary historical consolidated financial information of (i) NRG as of and for the year ended December 31, 2004 and as of and for the nine months ended September 30, 2005, (ii) Texas Genco as of and for the year ended December 31, 2004 and as of and for the nine months ended September 30, 2005, and (iii) the combined company on a pro forma basis for the year ended December 31, 2004 and as of and for the nine months ended September 30, 2005, giving effect to (a) the reclassification of Audrain as a discontinued operation; see “—Recent Developments”; (b) the inclusion of the results pursuant to the ROFR (as described below); (c) the refinancing of NRG’s old debt structure; (d) the remaining Financing Transactions and subsequent Acquisition; and (e) the acquisition of the remaining 50% ownership interest in WCP Holdings and the sale of our 50% ownership interest in Rocky Road; see “—Recent Developments”.

      The summary historical consolidated financial information of NRG as of and for the year ended December 31, 2004 were derived from the audited consolidated financial information contained in the audited consolidated financial statements of NRG incorporated by reference in this prospectus supplement. The summary unaudited historical consolidated financial information for NRG as of and for the nine months ended September 30, 2005 (i) were derived from NRG’s unaudited consolidated financial statements which are incorporated by reference into this prospectus supplement, (ii) have been prepared on a similar basis to that used in the preparation of the audited financial statements of NRG and (iii) in the opinion of NRG’s management, include all adjustments necessary for a fair statement of the results for the unaudited interim period. The results for periods for less than a full year are not necessarily indicative of the results to be expected for any interim period.

      The summary historical consolidated financial information of Texas Genco as of and for the year ended December 31, 2004 were derived from the audited consolidated financial information contained in the audited consolidated financial statements of Texas Genco incorporated by reference into this prospectus supplement. The summary unaudited historical consolidated financial information for Texas Genco as of and for the nine months ended September 30, 2005 (i) were derived from Texas Genco’s unaudited financial statements which are incorporated by reference into this prospectus supplement, (ii) have been prepared on a similar basis to that used in the preparation of the audited financial statements of Texas Genco, and (iii) in the opinion of Texas Genco’s management, include all adjustments necessary for a fair statement of the results for the unaudited interim period. The results for periods for less than a full year are not necessarily indicative of the results to be expected for any interim period.

      The historical financial information for WCP as of and for the year ended December 31, 2004 were derived from the audited financial statements of WCP as of and for the year ended December 31, 2004 contained as Exhibit 99.1 in NRG’s Form 10-K filed on March 30, 2005. The unaudited historical consolidated financial information as of and for the nine months ended September 30, 2005 (i) have been derived from WCP’s unaudited condensed consolidated financial statements that are included as Exhibit 99.06 to the current report on Form 8-K/A filed on January 5, 2006, (ii) have been prepared on a similar basis to that used in the preparation of the audited financial statements and (iii) in the opinion of WCP’s management, include all adjustments necessary for a fair statement of the results for the unaudited interim period.

      The unaudited pro forma combined income statement data and other financial data for the combined company for the year ended December 31, 2004 and for the nine months ended September 30, 2005 give effect to (a) the reclassification of Audrain as a discontinued operation; (b) the inclusion of the results pursuant to the ROFR; (c) the refinancing of NRG’s old debt structure; (d) the remaining Financing Transactions and subsequent Acquisition; and (e) the acquisition of the remaining 50% ownership interest in WCP Holdings and the sale of our 50% ownership interest in Rocky Road, as if they had occurred on January 1, 2004. The unaudited pro forma combined balance sheet data as of September 30, 2005 gives effect to (a) the sale of Audrain as of September 30, 2005; (b) the refinancing of NRG’s old debt structure; (c) the remaining Financing Transactions and subsequent Acquisition; and (d) the acquisition of the remaining 50% ownership interest in WCP Holdings and the sale of our 50% ownership interest in Rocky Road as if they had occurred on September 30, 2005. The adjustments reflected in the unaudited pro forma financial data are

based on available information and assumptions management believes are reasonable. However, due to the lack of asset appraisals and a future closing date, it is difficult to estimate a pro forma allocation of purchase price for the Acquisition. For purposes of these pro forma statements we have assumed that the consideration paid in excess of the historical book value of net assets acquired is related to the step-up in fair value of Texas Genco’s emission credit inventory, a step-up in the value of Texas Genco’s fixed assets, and an increase in liabilities for assumed out-of-market contracts. Once the Acquisition is closed, the excess of the estimated purchase price may differ considerably from these assumptions based on the results of appraisals and the finalization of the purchase price allocation as a result of closing and other analyses, which NRG is obtaining. The other analyses include actuarial studies of employee benefit plans, income tax effects of the Acquisition, analyses of operations to identify assets for disposition and the evaluation of staffing requirements necessary to meet future business needs. Ultimately, the excess of the purchase price over the fair value of the net tangible and identified intangible assets acquired will be recorded as goodwill.

      The unaudited pro forma financial information is for informational purposes only, however, and is based on several assumptions, including our assumptions regarding the Financing Transactions and the Acquisition, that may prove to be inaccurate. The unaudited pro forma consolidated financial data presented below do not purport to represent what the combined company’s results of operations would actually have been had the Acquisition and the Financing Transactions in fact occurred on the dates specified above or to project the combined company’s results of operations for any future period.

      The historical consolidated financial information and the unaudited pro forma combined financial information set forth below should be read in conjunction with (i) the consolidated financial statements of NRG, the related notes thereto and Management’s Discussion and Analysis of Financial Condition and Results of Operations included in NRG’s annual report for the year ended December 31, 2004 as amended by the current report on Form 8-K filed on December 20, 2005, and quarterly report on Form 10-Q for the nine months ended September 30, 2005, each as incorporated in this prospectus supplement by reference, (ii) the consolidated financial statements of Texas Genco and Texas Genco Holdings, Inc., the related notes thereto and Management’s Discussion and Analysis of Financial Condition and Results of Operations for the year ended December 31, 2004 and for the nine months ended September 30, 2005, each as incorporated in this prospectus supplement by reference to NRG’s current report on Form 8-K filed on December 21, 2005, (iii) the financial statements of WCP, the related notes thereto included in NRG’s annual report on Form 10-K as Exhibit 99.1 as of and for the year ended December 31, 2004 and the financial statements as of and for the nine months ended September 30, 2005 as found in Exhibit 99.06 to the current report on Form 8-K/A filed on January 5, 2006 and (iv) “Selected Consolidated Financial Information of NRG,” “Selected Consolidated Financial Information of Texas Genco,” “Risk Factors— Risks Related to the Acquisition— Because the historical and pro forma financial information incorporated by reference or included elsewhere in this prospectus supplement may not be representative of our results as a combined company or capital structure after the Acquisition, and NRG’s and Texas Genco’s historical financial information are not comparable to their current financial information, you have limited financial information on which to evaluate us, NRG, Texas Genco and your investment decision,” and “Risk Factors— Risks Related to the Offering— If NRG is unable to raise sufficient proceeds through other Financing Transactions described elsewhere in this prospectus supplement, NRG may draw down on a bridge loan facility in order to close the Acquisition which would significantly increase our indebtedness. If NRG elects not to consummate the financing under the bridge loan facility, NRG may seek alternative sources of financing for the Acquisition, the terms of which are unknown to us and could limit our ability to operate our business” elsewhere in this prospectus supplement. In addition, no assurance can be given that the Acquisition will be consummated in accordance with the anticipated timing or at all. See “Risk Factors— Risks Related to the Offering— There can be no assurance that the Acquisition will be consummated in accordance with the anticipated timing or at all, and the closing of this offering is not conditioned on the consummation of the Acquisition. If the Acquisition is not consummated, NRG’s common stock, and therefore our mandatory convertible preferred stock, will not reflect any actual or anticipated interest in Texas Genco, and if the Acquisition is delayed, this interest will not be reflected during the period of delay.”

RISK FACTORS

      Investing in our common stock involves a high degree of risk. The risks below are not the only risks that we face. Additional risks and uncertainties not currently known to us or that we currently deem to be immaterial may also materially adversely affect our business operations. The following risks could affect our business, financial condition or results of operations. In such a case, you may lose all or part of your original investment. You should carefully consider the risks described below as well as other information and data set forth in this prospectus supplement, the accompanying prospectus and the documents incorporated by reference herein and therein before making an investment decision with respect to the common stock.

Risks Related to the Operation of our Business

      Many of our facilities operate as “merchant” facilities without long-term power sale agreements, and therefore are exposed to market fluctuations. Without the benefit of long-term power purchase agreements for certain assets, we cannot be sure that we will be able to sell any or all of the power generated by these facilities at commercially attractive rates or that these facilities will be able to operate profitably. This could lead to future impairments of our property, plant and equipment or to the closing of certain of our facilities resulting in economic losses and liabilities, which could have a material adverse effect on our results of operations, financial condition or cash flows.

      A significant percentage of the combined company’s domestic revenues is derived from baseload power plants that are fueled by coal or nuclear fuel. In many of the competitive markets where NRG and Texas Genco operate, the price of power typically is set by marginal cost natural gas-fired and oil-fired power plants that currently have substantially higher variable costs than our solid fuel baseload power plants. This tends to increase the market clearing price for power. The current pricing and cost environment allows NRG’s and Texas Genco’s baseload coal and nuclear fuel generation assets to earn attractive operating margins compared to plants fueled by natural gas and oil. A decrease in oil and natural gas prices could be expected to result in a corresponding decrease in the market price of power but would generally not affect the cost of the solid fuels that NRG and Texas Genco use. This could significantly reduce the operating margins of NRG’s and Texas Genco’s baseload generation assets and materially and adversely impact NRG’s and Texas Genco’s financial performance.

      We sell all or a portion of the energy, capacity and other products from many of our facilities to wholesale power markets, including energy markets operated by independent system operators, or ISOs, or regional transmission organizations, or RTOs, as well as wholesale purchasers. We are generally not entitled to traditional cost-based regulation, therefore we sell electric generation capacity, power and ancillary services to wholesale purchasers at prices determined by the market. As a result, we are not guaranteed any rate of return on our capital investments through mandated rates, and our revenues and results of operations depend upon current and forward market prices for power.

      Market prices for power, generation capacity and ancillary services tend to fluctuate substantially. Unlike most other commodities, electric power can only be stored on a very limited basis and generally must be produced concurrently with its use. As a result, power prices are subject to significant volatility from supply and demand imbalances, especially in the day-ahead and spot markets. Long-term and short-term power prices may also fluctuate substantially due to other factors outside of our control, including:

      These factors have caused NRG’s and Texas Genco’s quarterly operating results to fluctuate in the past and will continue to cause them to do so in the future.

      We rely on coal, nuclear fuel derived from uranium, oil and natural gas to fuel our power generation facilities. Delivery of these fuels to our facilities is dependent upon the continuing financial viability of contractual counterparties as well as upon the infrastructure (including rail lines, rail cars, barge facilities, roadways, and natural gas pipelines) available to serve each generation facility. As a result, we are subject to the risks of disruptions or curtailments in the production of power at our generation facilities if a counterparty fails to perform or if there is a disruption in the fuel delivery infrastructure.

      The combined company has sold forward a substantial part of its baseload power in order to lock in long-term prices that it deemed to be favorable at the time it entered into the forward sale contracts. In order to hedge our obligations under these forward power sales contracts, we have entered into long-term and short-term contracts for the purchase and delivery of fuel. Many of our forward power sales contracts do not allow us to pass through changes in fuel costs or discharge the company’s power sale obligations in the case of a disruption in fuel supply due to force majeure events or the default of a fuel supplier or transporter. Disruptions in our fuel supplies may therefore require us to find alternative fuel sources at higher costs, to find other sources of power to deliver to counterparties at higher cost, or to pay damages to counterparties for failure to deliver power as contracted. Any such event could have a material adverse effect on our financial performance.

      We also buy significant quantities of fuel on a short-term or spot market basis. Prices for all of our fuels fluctuate, sometimes rising or falling significantly over a short period. The price we can obtain for the sale of energy may not rise at the same rate, or may not rise at all, to match a rise in fuel or delivery costs. This may have a material adverse effect on our financial performance. Changes in market prices for natural gas, coal and oil may result from the following:

      Our plant operating characteristics and equipment, particularly at our coal-fired plants, often dictate the specific fuel quality to be combusted. The availability and price of specific fuel qualities may vary due to supplier financial or operational disruptions, transportation disruptions and force majeure. At times, coal of specific quality may not be available at any price, or we may not be able to transport such coal to our facilities on a timely basis. In such case, we may not be able to run a coal facility even if it would be profitable. Operating a coal facility with lesser quality coal can lead to emission or operating problems. If we had sold forward the power from such a coal facility, we could be required to supply or purchase power from alternate sources, perhaps at a loss. This could have a material adverse impact on the financial results of specific plants and on our results of operations.

      Texas Genco procures approximately 70% of the fuel for its Limestone facility from a lignite mine adjacent to the plant, pursuant to a contract that expires in 2015. The contract has been the subject of past litigation over pricing and other matters, and requires the parties periodically to renegotiate both the price and volume of lignite provided. If we are unable to renegotiate the terms of the agreement, if the counterparty fails to perform, or if the mine is unable to yield sufficient quantities of lignite, we could experience a disruption of supply, which could result in a curtailment or shutdown of the Limestone plant, or could require us to acquire the fuel at higher spot market prices.

      The owners (including Texas Genco) of STP satisfy fuel supply requirements for STP by acquiring uranium concentrates and contracting to convert uranium concentrates into uranium hexafluoride, enrich uranium hexafluoride and fabricate nuclear fuel assemblies. These contracts have varying expiration dates, and most are short to medium term. A disruption in uranium supplies, or in conversion, enrichment or fabrication services, could adversely affect operations at STP or increase the fuel costs associated with operations.

      A substantial portion of the output from NRG’s units is sold forward under fixed price power sales contracts through 2010, and we also sell forward the output from our intermediate and peaking facilities when we deem it commercially advantageous to do so. Because our obligations under most of these agreements are not contingent on a unit being available to generate power, we are generally required to deliver power to the buyer, even in the event of a plant outage, fuel supply disruption or a reduction in the available capacity of the unit. To the extent that we do not have sufficient lower cost capacity to meet our commitments under our forward sales obligations, we would be required to supply replacement power either by running our other, higher cost power plants or by obtaining power from third-party sources at market prices that could substantially exceed the contract price. If we failed to deliver the contracted power, then we would be required to pay the difference between the market price at the delivery point and the contract price, and the amount of such payments could be substantial.

      In NRG’s South Central region, NRG has long-term contracts with rural cooperatives that require it to serve all of the cooperatives’ requirements at prices that generally reflect the costs of coal-fired generation. At times, the output from NRG’s coal-fired Big Cajun II facility is inadequate to serve these obligations, and when that happens NRG typically purchases power from other power producers, often at a loss. NRG’s financial returns from its South Central region are likely to deteriorate over time as the rural cooperatives grow

their customer bases, unless NRG is able to amend or renegotiate its contracts with the cooperatives or add generating capacity.

      We enter into hedging agreements, including contracts to purchase or sell commodities at future dates and at fixed prices, in order to manage the commodity price risks inherent in our power generation operations. These activities, although intended to mitigate price volatility, expose us to other risks. When we sell power forward, we give up the opportunity to sell power at higher prices in the future, which not only may result in lost opportunity costs but also may require us to post significant amounts of cash collateral or other credit support to our counterparties. Further, if the values of the financial contracts change in a manner we do not anticipate, or if a counterparty fails to perform under a contract, it could harm our business, operating results or financial position.

      We do not typically hedge the entire exposure of our operations against commodity price volatility. To the extent we do not hedge against commodity price volatility, our results of operations and financial position may be improved or diminished based upon movement in commodity prices.

      From time to time we may engage in trading activities, including the trading of power, fuel and emissions credits, that are not directly related to the operation of our generation facilities or the management of related risks. These trading activities take place in volatile markets and some of these trades could be characterized as speculative. We would expect to settle these trades financially rather than through the production of power or the delivery of fuel. This trading activity may expose us to the risk of significant financial losses which could have a material adverse effect on our business and financial condition.

      We are exposed to market risks through our power marketing business, which involves the sale of energy, capacity and related products and the purchase and sale of fuel, transmission services and emission allowances. These market risks include, among other risks, volatility arising from location and timing differences that may be associated with buying and transporting fuel, converting fuel into energy and delivering the energy to a buyer.

      We undertake these marketing activities through agreements with various counterparties. Many of our agreements with counterparties include provisions that require us to provide guarantees, offset of netting arrangements, letters of credit, a second lien on assets and/or cash collateral to protect the counterparties against the risk of our default or insolvency. The amount of such credit support that must be provided typically is based on the difference between the price of the commodity in a given contract and the market price of the commodity. Significant movements in market prices can result in our being required to provide cash collateral and letters of credit in very large amounts. The effectiveness of our strategy may be dependent on the amount of collateral available to enter into or maintain these contracts, and liquidity requirements may be greater than we anticipate or are able to meet. Without a sufficient amount of working capital to post as collateral in support of performance guarantees or as cash margin, we may not be able to manage price volatility effectively or to implement our strategy. An increase in demands from our counterparties to post letters of credit or cash collateral may negatively affect our liquidity position and financial condition.

      Further, if our facilities experience unplanned outages, we may be required to procure replacement power at spot market prices in order to fulfill contractual commitments. Without adequate liquidity to post margin and collateral requirements, we may be exposed to significant losses, may miss significant opportunities, and may have increased exposure to the volatility of spot markets.

      We engage in commodity-related marketing and price-risk management activities in order to economically hedge our exposure to market risk with respect to:

      We generally attempt to balance our fixed-price physical and financial purchases and sales commitments in terms of contract volumes and the timing of performance and delivery obligations, through the use of financial and physical derivative contracts. These derivatives are accounted for in accordance with SFAS No. 133, “Accounting for Derivative Instruments and Hedging Activities,” as amended by SFAS No. 137, SFAS No. 138 and SFAS No. 149. SFAS No. 133 requires us to record all derivatives on the balance sheet at fair value with changes in the fair value resulting from fluctuations in the underlying commodity prices immediately recognized in earnings, unless the derivative qualifies for hedge accounting treatment. Whether a derivative qualifies for hedge accounting depends upon it meeting specific criteria used to determine if hedge accounting is and will remain appropriate for the term of the derivative. Economic hedges will not necessarily qualify for hedge accounting treatment. As a result, we are unable to predict the impact that our risk management decisions may have on our quarterly and annual operating results.

      NRG will account for the Acquisition using the purchase method of accounting. The purchase price for Texas Genco will be allocated to identifiable tangible and intangible assets and assumed liabilities based on estimated fair values at the date of consummation of the Acquisition. Any unallocated portion of the purchase price will be allocated to goodwill. On a pro forma basis, approximately 23% of the pro forma combined company’s total assets will be goodwill and other intangibles, of which approximately $2.4 billion will be goodwill. In accordance with Financial Accounting Standard No. 142, “Goodwill and Other Intangible Assets,” goodwill is not amortized but is reviewed annually or more frequently for impairment and other intangibles are also reviewed at least annually or more frequently, if certain conditions exist, and may be amortized. Any reduction in or impairment of the value of goodwill or other intangible assets will result in a charge against earnings which could materially adversely affect our reported results of operations and financial position in future periods.

      We have numerous competitors in all aspects of our business, and additional competitors may enter the industry. Because many of our facilities are old, newer plants owned by our competitors are often more efficient than our aging plants, which may put some of our plants at a competitive disadvantage to the extent our competitors are able to consume the same fuel as we consume at those plants. Over time, our plants may be squeezed out of their markets, or may be unable to compete with these more efficient plants.

      In our power marketing and commercial operations, we compete on the basis of our relative skills, financial position and access to capital with other providers of electric energy in the procurement of fuel and transportation services, and the sale of capacity, energy and related products. In order to compete successfully, we seek to aggregate fuel supplies at competitive prices from different sources and locations and to efficiently utilize transportation services from third-party pipelines, railways and other fuel transporters and transmission services from electric utilities.

      Other companies with which we compete may have greater liquidity, access to credit and other financial resources, lower cost structures, more effective risk management policies and procedures, greater ability to incur losses, longer-standing relationships with customers, greater potential for profitability from ancillary services or greater flexibility in the timing of their sale of generation capacity and ancillary services than we do.

      Our competitors may be able to respond more quickly to new laws or regulations or emerging technologies, or to devote greater resources to the construction, expansion or refurbishment of their power generation facilities than we can. In addition, current and potential competitors may make strategic acquisitions or establish cooperative relationships among themselves or with third parties. Accordingly, it is possible that new competitors or alliances among current and new competitors may emerge and rapidly gain significant market share. There can be no assurance that we will be able to compete successfully against current and future competitors, and any failure to do so would have a material adverse effect on our business, financial condition, results of operations and cash flow. See “Business— Competition.”

      The ongoing operation of our facilities involves risks that include the breakdown or failure of equipment or processes, performance below expected levels of output or efficiency and the inability to transport our product to our customers in an efficient manner due to a lack of transmission capacity. Unplanned outages of generating units, including extensions of scheduled outages due to mechanical failures or other problems occur from time to time and are an inherent risk of our business. Unplanned outages typically increase our operation and maintenance expenses and may reduce our revenues as a result of selling fewer MWh or require us to incur significant costs as a result of running one of our higher cost units or obtaining replacement power from third parties in the open market to satisfy our forward power sales obligations. Our inability to operate our plants efficiently, manage capital expenditures and costs, and generate earnings and cash flow from our asset-based businesses in relation to our debt and other obligations could have a material adverse effect on our results of operations, financial condition or cash flows.

      While we maintain insurance, obtain warranties from vendors and obligate contractors to meet certain performance levels, the proceeds of such insurance, warranties or performance guarantees may not be adequate to cover our lost revenues, increased expenses or liquidated damages payments should we experience equipment breakdown or non-performance by contractors or vendors.

      Many of our facilities are old and are likely to require periodic upgrade and improvement. Any unexpected failure, including failure associated with breakdowns, forced outages or any unanticipated capital expenditures, could result in reduced profitability.

      We cannot be certain of the level of capital expenditures that will be required due to changing environmental and safety laws and regulations (including changes in the interpretation or enforcement thereof), needed facility repairs and unexpected events (such as natural disasters or terrorist attacks). The unexpected requirement of large capital expenditures could have a material adverse effect on our financial performance and condition.

      If we make any major modifications to our power generation facilities, we may be required to install the best available control technology or to achieve the lowest achievable emissions rate, as such terms are defined under the new source review provisions of the federal Clean Air Act. Any such modifications would likely result in substantial additional capital expenditures.

      We may also choose to undertake the repowering, refurbishment or upgrading of current facilities based on our assessment that such activity will provide adequate financial returns. Such projects often require several years of development and capital expenditures before commencement of commercial operations, and key

assumptions underpinning a decision to make such an investment may prove incorrect, including assumptions regarding construction costs, timing, available financing and future fuel and power prices. The construction, expansion, modification and refurbishment of power generation facilities involve many additional risks, including:

      Any of these risks could cause our financial returns on new investments to be lower than expected, or could cause us to operate below expected capacity or availability levels, which could result in lost revenues, increased expenses, higher maintenance costs and penalties.

      We often rely on a single contracted supplier or a small number of suppliers for the provision of fuel, transportation of fuel and other services required for the operation of certain of our facilities. If these suppliers cannot perform, we utilize the marketplace to provide these services. There can be no assurance that the marketplace can provide these services.

      At times, we rely on a single customer or a few customers to purchase all or a significant portion of a facility’s output, in some cases under long-term agreements that account for a substantial percentage of the anticipated revenue from a given facility. We have hedged a portion of our exposure to power price fluctuations through forward fixed price power sales and natural gas price swap agreements. Counterparties to these agreements may breach or may be unable to perform their obligations. We may not be able to enter into replacement agreements on terms as favorable as our existing agreements, or at all. If we were unable to enter into replacement power purchase agreements, we would sell our plants’ power at market prices. If we were unable to enter into replacement fuel or fuel transportation purchase agreements, we would seek to purchase our plants’ fuel requirements at market prices, exposing us to market price volatility and the risk that fuel and transportation may not be available during certain periods at any price.

      In the past several years, a substantial number of companies, some of which serve as our counterparties from time to time, have experienced downgrades in their credit ratings. The failure of any supplier or customer to fulfill its contractual obligations to us could have a material adverse effect on our financial results. Consequently, the financial performance of our facilities is dependent on the credit quality of, and continued performance by, suppliers and customers.

      We depend on transmission facilities owned and operated by others to deliver the wholesale power we sell from our power generation plants to our customers. If transmission is disrupted, or if the transmission capacity

infrastructure is inadequate, our ability to sell and deliver wholesale power may be adversely impacted. If a region’s power transmission infrastructure is inadequate, our recovery of wholesale costs and profits may be limited. If restrictive transmission price regulation is imposed, the transmission companies may not have sufficient incentive to invest in expansion of transmission infrastructure. We also cannot predict whether transmission facilities will be expanded in specific markets to accommodate competitive access to those markets.

      In addition, in certain of the markets in which we operate, energy transmission congestion may occur and we may be deemed responsible for congestion costs if we schedule delivery of power between congestion zones during times when congestion occurs between the zones. If we are liable for congestion costs, our financial results could be adversely affected.

      In the ERCOT, California ISO, New York ISO and New England ISO markets, the combined company will have a significant amount of generation located in load pockets making that generation valuable, particularly with respect to maintaining the reliability of the transmission grid. Expansion of transmission systems to reduce or eliminate these load pockets could negatively impact the value or profitability of our existing facilities in these areas.

      We have limited control over the operation of some project investments and joint ventures because our investments are in projects where we beneficially own less than a majority of the ownership interests. We seek to exert a degree of influence with respect to the management and operation of projects in which we own less than a majority of the ownership interests by negotiating to obtain positions on management committees or to receive certain limited governance rights, such as rights to veto significant actions. However, we may not always succeed in such negotiations. We may be dependent on our co-venturers to operate such projects. Our co-venturers may not have the level of experience, technical expertise, human resources management and other attributes necessary to operate these projects optimally. The approval of co-venturers also may be required for us to receive distributions of funds from projects or to transfer our interest in projects.

      We may seek to acquire additional companies or assets in our industry. The acquisition of power generation companies and assets is subject to substantial risks, including the failure to identify material problems during due diligence, the risk of over-paying for assets and the inability to arrange financing for an acquisition as may be required or desired. Further, the integration and consolidation of acquisitions requires substantial human, financial and other resources and, ultimately, our acquisitions may not be successfully integrated. There can be no assurances that any future acquisitions will perform as expected or that the returns from such acquisitions will support the indebtedness incurred to acquire them or the capital expenditures needed to develop them.

      Power generation involves hazardous activities, including acquiring, transporting and unloading fuel, operating large pieces of rotating equipment and delivering electricity to transmission and distribution systems. In addition to natural risks such as earthquake, flood, lightning, hurricane and wind, other hazards, such as fire, explosion, structural collapse and machinery failure are inherent risks in our operations. These and other hazards can cause significant personal injury or loss of life, severe damage to and destruction of property, plant and equipment, contamination of, or damage to, the environment and suspension of operations. The occurrence of any one of these events may result in our being named as a defendant in lawsuits asserting claims for substantial damages, including for environmental cleanup costs, personal injury and property damage and fines and/or penalties. We maintain an amount of insurance protection that we consider adequate, but we cannot assure you that our insurance will be sufficient or effective under all circumstances

and against all hazards or liabilities to which we may be subject. A successful claim for which we are not fully insured could hurt our financial results and materially harm our financial condition. Further, due to rising insurance costs and changes in the insurance markets, we cannot assure you that insurance coverage will continue to be available at all or at rates or on terms similar to those presently available to us. Any losses not covered by insurance could have a material adverse effect on our financial condition, results of operations or cash flows.

      Our business is subject to extensive foreign, federal, state and local laws and regulation. Compliance with the requirements under these various regulatory regimes may cause us to incur significant additional costs and failure to comply with such requirements could result in the shutdown of the non-complying facility, the imposition of liens, fines and/or civil or criminal liability.

      Public utilities under the Federal Power Act, or FPA, are required to obtain the Federal Energy Regulatory Commission’s, or FERC’s, acceptance of their rate schedules for wholesale sales of electricity. All of NRG’s non-qualifying facility generating companies and power marketing affiliates in the United States make sales of electricity in interstate commerce and are public utilities for purposes of the FPA. FERC has granted each of NRG’s generating and power marketing companies the authority to sell electricity at market-based rates. The FERC’s orders that grant NRG’s generating and power marketing companies market-based rate authority reserve the right to revoke or revise that authority if FERC subsequently determines that NRG can exercise market power in transmission or generation, create barriers to entry or engage in abusive affiliate transactions. In addition, NRG’s market-based sales are subject to certain market behavior rules and, if any of NRG’s generating and power marketing companies were deemed to have violated one of those rules, they are subject to potential disgorgement of profits associated with the violation and/or suspension or revocation of their market-based rate authority. If NRG’s generating and power marketing companies were to lose their market-based rate authority, such companies would be required to obtain FERC’s acceptance of a cost-of-service rate schedule and would become subject to the accounting, record-keeping and reporting requirements that are imposed on utilities with cost-based rate schedules. This could have an adverse effect on the rates NRG charges for power from its facilities.

      We are also affected by changes to market rules, tariffs, changes in market structures, changes in administrative fee allocations and changes in market bidding rules that occur in the existing ISOs and RTOs. The ISOs and RTOs that oversee most of the wholesale power markets impose, and in the future may continue to impose, price limitations, offer caps, and other mechanisms to address some of the volatility and the potential exercise of market power in these markets. These types of price limitations and other regulatory mechanisms may adversely affect the profitability of our generation facilities that sell energy and capacity into the wholesale power markets. In addition, the regulatory and legislative changes that have recently been enacted at the federal level and in a number of states in an effort to promote competition are novel and untested in many respects. These new approaches to the sale of electric power have very short operating histories, and it is not yet clear how they will operate in times of market stress or pressure, given the extreme volatility and lack of meaningful long-term price history in many of these markets and the imposition of price limitations by independent system operators.

      Similarly, the Texas Genco subsidiaries are registered as power generation companies with the Public Utility Commission of Texas, or PUCT. PUCT has jurisdiction with respect to the mitigation of undue market power and has authority to remedy market power abuses in the ERCOT market, both directly and, indirectly, through oversight of ERCOT. PUCT has proposed a significant change in the rules governing the ERCOT market. Specifically the PUCT adopted a rule directing the ERCOT ISO to develop and implement a wholesale market that, among other things, replaces the existing zonal market design with a nodal market design based on locational marginal prices for power. The market redesign project is expected to take effect in 2009. We expect that implementation of any new market design will require modification to our procedures and systems. We do not know for certain how the planned market restructuring will affect our revenues, and

some of the combined company’s plants in ERCOT may experience adverse pricing effects due to their location on the transmission grid.

      Under the Atomic Energy Act of 1954, as amended, or AEA, operation of STP, of which Texas Genco owns indirectly a 44.0% interest, is subject to regulation by the Nuclear Regulatory Commission, or NRC. Such regulation includes licensing, inspection, enforcement, testing, evaluation and modification of all aspects of nuclear reactor power plant design and operation, environmental and safety performance, technical and financial qualifications, decommissioning funding assurance and transfer and foreign ownership restrictions. Texas Genco’s 44.0% share of the output of STP represents approximately 1,101 MW of generation capacity, which is approximately 10% of the total gross generation capacity owned by Texas Genco.

      There are unique risks to owning and operating a nuclear power facility. These include liabilities related to the handling, treatment, storage, disposal, transport, release and use of radioactive materials, particularly with respect to spent nuclear fuel, and uncertainties regarding the ultimate, and potential exposure to, technical and financial risks associated with modifying or decommissioning a nuclear facility. The NRC could require the shutdown of the plant for safety reasons or refuse to permit restart of the unit after unplanned or planned outages. New or amended NRC safety and regulatory requirements may give rise to additional operation and maintenance costs and capital expenditures. STP may be obligated to continue storing spent nuclear fuel if the Department of Energy continues to fail to meet its contractual obligations to STP made pursuant to the U.S. Nuclear Waste Policy Act of 1982 to accept and dispose of STP’s spent nuclear fuel. See “Business— Environmental Matters— U.S. Federal Environmental Initiatives— Nuclear Waste.” Costs associated with these risks could be substantial and have a material adverse effect on our results of operations, financial condition or cash flow. In addition, to the extent that all or a part of STP is required by the NRC to permanently or temporarily shut down or modify its operations, or is otherwise subject to a forced outage, Texas Genco may incur additional costs to the extent it is obligated to provide power from more expensive alternative sources— either Texas Genco’s own plants, third party generators or the ERCOT— to cover Texas Genco’s then existing forward sale obligations. Such shutdown or modification could also lead to substantial costs related to the storage and disposal of radioactive materials and spent nuclear fuel.

      Texas Genco and the other owners of STP maintain nuclear property and nuclear liability insurance coverage as required by law. The Price-Anderson Act, as amended by the Energy Policy Act of 2005, requires owners of nuclear power plants in the United States to be collectively responsible for retrospective secondary insurance premiums for liability to the public arising from nuclear incidents resulting in claims in excess of the required primary insurance coverage amount of $300 million per reactor. The Price-Anderson Act only covers nuclear liability associated with any accident in the course of operation of the nuclear reactor, transportation of nuclear fuel to the reactor site, in the storage of nuclear fuel and waste at the reactor site and the transportation of the spent nuclear fuel and nuclear waste from the nuclear reactor. All other non-nuclear liabilities are not covered. Any substantial retrospective premiums imposed under the Price-Anderson Act or losses not covered by insurance could have a material adverse effect on our financial condition, results of operations or cash flows.

      Our business is subject to the environmental laws and regulations of foreign, federal, state and local authorities. We must comply with numerous environmental laws and regulations and obtain numerous governmental permits and approvals to operate our plants. If we fail to comply with any environmental requirements that apply to our operations, we could be subject to administrative, civil and/or criminal liability and fines, and regulatory agencies could take other actions seeking to curtail our operations. In addition, when new requirements take effect or when existing environmental requirements are revised, reinterpreted or subject

to changing enforcement policies, our business, results of operations, financial condition and cash flows could be adversely affected.

      Environmental laws and regulations have generally become more stringent over time, and we expect this trend to continue. In particular, the U.S. Environmental Protection Agency, or USEPA, has recently promulgated regulations requiring additional reductions in nitrogen oxides, or NO_x and sulfur dioxide, or SO₂, emissions, commencing in 2009 and 2010 respectively, and has also promulgated regulations requiring reductions in mercury emissions from coal-fired electric generating units, commencing in 2010 with more substantial reductions in 2018. These regulatory programs are currently subject to litigation and reconsideration by the USEPA, which could affect the timing of our future capital projects. See “Business— Environmental Matters— U.S. Federal Environmental Initiatives— Air.” Moreover, certain of the states in which we operate have promulgated air pollution control regulations which are more stringent than existing and proposed federal regulations. Ongoing public concerns about emissions of SO₂, NO_x, mercury and carbon dioxide and other greenhouse gases from power plants have resulted in proposed laws and regulations at the federal, state and regional levels that, if they were to take effect substantially as proposed, would likely apply to our operations. For example, we could incur substantial costs pursuant to the proposed multi-state carbon cap-and-trade program known as the Regional Greenhouse Gas Initiative, or RGGI, which would apply to the facilities in our Northeast region. A model rule for implementation of RGGI is expected to be released within the next few months. See “Business— Environmental Matters— Regional U.S. Environmental Regulatory Initiatives.”

      Significant capital expenditures may be required to keep our facilities compliant with environmental laws and regulations, and if it is not economical to make those capital expenditures then we may need to retire or mothball facilities, or restrict or modify our operations to comply with more stringent standards.

      Certain environmental laws impose strict, joint and several liability for costs required to clean up and restore sites where hazardous substances have been disposed or otherwise released. We are generally responsible for all liabilities associated with the environmental condition of our power generation plants, including any soil or groundwater contamination that may be present, regardless of when the liabilities arose and whether the liabilities are known or unknown, or arose from the activities of our predecessors or third parties. We are currently subject to remediation obligations at a number of our facilities. See “Business— Environmental Matters— Domestic Site Remediation Matters.”

      Our facilities and related properties may become subject to decommissioning and/or site remediation obligations that may require material unplanned expenditures or otherwise materially affect the value of those assets. The closure or modification of any of our facilities, especially with respect to STP, could lead to substantial liabilities, including related to the cleanup of any contamination that occurred during the facility’s operation. While we believe that we meet, or are performing, all site remediation obligations currently applicable to our assets (including through the provision of various forms of financial assurance at certain facilities at which we are not currently required to perform remediation), more onerous obligations often apply to sites where a plant is to be dismantled, which could negatively affect our ability to economically undertake power redevelopments or alternate uses at existing power plant sites. Further, laws and regulations may change to impose material additional decommissioning and remediation obligations on us in the future, negatively impacting the value of our assets and/or our ability to undertake redevelopment projects.

      As of September 30, 2005, after giving pro forma effect to the Acquisition, approximately 46.8% of the combined company’s employees at its U.S. generation plants would have been covered by collective bargaining agreements, and 774 employees of the combined company’s plants in Texas are covered by a single collective bargaining agreement that expires in September 2006. In the event that our union employees strike,

participate in a work stoppage or slowdown or engage in other forms of labor strife or disruption, we would be responsible for procuring replacement labor or we could experience reduced power generation or outages. Our ability to procure such labor is uncertain. Strikes, work stoppages or the inability to negotiate future collective bargaining agreements on favorable terms could have a material adverse effect on our business, financial condition, results of operations and cash flows.

      Research and development activities are ongoing to provide alternative and more efficient technologies to produce power, including fuel cells, clean coal and coal gasification, microturbines, photovoltaic (solar) cells and improvements in traditional technologies and equipment, such as more efficient gas turbines. Advances in these or other technologies could reduce the costs of power production to a level below what we have currently forecasted, which could adversely affect our revenue, results of operations or competitive position.

      Our generation facilities and the facilities of third parties on which they rely may be targets of terrorist activities, as well as events occurring in response to or in connection with them, that could cause environmental repercussions and/or result in full or partial disruption of their ability to generate, transmit, transport or distribute electricity or natural gas. Strategic targets, such as energy-related facilities, may be at greater risk of future terrorist activities than other domestic targets. Any such environmental repercussions or disruption could result in a significant decrease in revenues or significant reconstruction or remediation costs, which could have a material adverse effect on our financial condition, results of operations and cash flows.

      We have investments in power projects in Australia, Germany and Brazil. International investments are subject to risks and uncertainties relating to the political, social and economic structures of the countries in which we invest. Risks specifically related to our investments in international projects may include:

      Many of Texas Genco’s plants have been subject to personal injury claims arising out of alleged exposure to asbestos. Most of the claimants who have brought such claims have been third-party workers who participated in the construction, renovation or repair of various industrial plants, including power plants. While many of the claimants have never worked at or near Texas Genco’s plants, some of the claimants have worked at locations owned by Texas Genco. While Texas Genco has been dismissed from many of these lawsuits without having to make any payment to claimants, Texas Genco has incurred and expects to continue to incur settlement costs associated with these claims. NRG is also subject to claims for asbestos exposure in certain of its facilities, as well as claims for indemnity from previous owners of those facilities. We defend against these claims aggressively, and, thus, we have incurred and expect to continue to incur defense costs as a result of such claims. For further discussion of such claims, see “Business— Legal Proceedings.”

      If asbestos-related claims against us rise significantly, our liability may be substantial. Moreover, if insurance currently available for contribution to the payment of asbestos liabilities becomes unavailable

(through insurer insolvencies, coverage disputes, changes in law or otherwise), asbestos liabilities could impact our results of operations, financial condition and cash flows.

      Our substantial debt could have important consequences for you, including:

      The indenture for the New Senior Notes contains, and our new credit facility will contain, financial and other restrictive covenants that will limit our ability to engage in activities that may be in our long-term best interests. Our failure to comply with those covenants could result in an event of default which, if not cured or waived, could result in the acceleration of all of our borrowed indebtedness.

      In addition, our ability to arrange financing, either at the corporate level or at a non-recourse project-level subsidiary, and the costs of such capital are dependent on numerous factors, including:

      We may not be successful in obtaining additional capital for these or other reasons. The failure to obtain additional capital from time to time may have a material adverse effect on our business and operations.

Risks Related to the Acquisition

      The success of the Acquisition will depend largely on NRG’s ability to consolidate and effectively integrate Texas Genco’s assets, operations and employees into NRG. The integration will require substantial time and attention from our management. If the integration takes longer or is more complex or expensive than anticipated, or if we cannot operate our combined business as effectively as we anticipate, our operating performance and profitability could be materially adversely affected.

      Texas Genco’s power generation assets operate in the ERCOT market, a market in which NRG does not currently operate. Accordingly, we are dependent upon Texas Genco’s existing managers and employees to manage those assets, and the loss of key Texas Genco managers or employees could adversely affect our business.

      In addition, as a result of the Acquisition, we have assumed all of Texas Genco’s liabilities. After the Acquisition, we may learn additional information about Texas Genco’s business that adversely affects us, such as unknown or contingent liabilities, issues relating to internal controls over financial reporting and issues relating to compliance with applicable laws.

      NRG’s financial statements prior to December 5, 2003 are not comparable to its financial statements after that date. As a result of NRG’s emergence from bankruptcy, it is operating its business with a new capital structure, and is subject to Fresh Start reporting requirements prescribed by generally accepted accounting principles in the United States. As required by Fresh Start reporting, assets and liabilities as of December 6, 2003 were recorded at fair value, with the enterprise value being determined in connection with the reorganization.

      Texas Genco did not exist prior to July 19, 2004, and Texas Genco and its subsidiaries had no operations and no material activities until December 15, 2004 when Texas Genco acquired its gas and coal-fired assets. Consequently, Texas Genco’s historical financial statements are not comparable to its current financial statements.

      NRG and Texas Genco have been operating as separate companies prior to the Acquisition. We have had no prior history as a combined entity and our operations have not previously been managed on a combined basis. Preparing the pro forma financial information contained in this prospectus supplement involved making several assumptions, such as the makeup of our capital structure after the consummation of the Financing Transactions. These assumptions may prove inaccurate. Therefore, the historical financial statements and pro forma financial statements incorporated by reference or presented in this prospectus supplement may not reflect what our results of operations, financial position and cash flows would have been had we operated on a combined basis and may not be indicative of what our results of operations, financial position and cash flows will be in the future.

      As a result, the historical and pro forma financial information incorporated by reference or included elsewhere in this prospectus supplement is of limited relevance to an investor in this offering. See “Selected Consolidated Financial Information of NRG” and “Selected Consolidated Financial Information of Texas Genco.” See also “—Risks Related to the Offering— If NRG is unable to raise sufficient proceeds through other Financing Transactions described elsewhere in this prospectus supplement, NRG may draw down on a bridge loan facility in order to close the Acquisition which would significantly increase our indebtedness. If NRG elects not to consummate the financing under the bridge loan facility, NRG may seek alternative sources of financing for the Acquisition, the terms of which are unknown to us and could limit our ability to operate our business.”

Risks Related to the Offering

      Although NRG expects to close the Acquisition in or about the first week of February 2006, there can be no assurance that the Acquisition will be completed in accordance with the anticipated timing or at all. In order to consummate the Acquisition, NRG and Texas Genco must obtain certain regulatory and other approvals and consents in a timely manner. If these approvals or consents are not received, or they are not received on terms that satisfy the conditions set forth in the Acquisition Agreement, then NRG and/or Texas Genco will not be obligated to complete the Acquisition. Also, NRG and/or Texas Genco may not receive these approvals or consents by the first week of February 2006, the current anticipated timing for closing the Acquisition. The Acquisition Agreement also contains customary and other closing conditions, which may not be satisfied or waived. In addition, under circumstances specified in the Acquisition Agreement, NRG or Texas Genco may terminate the Acquisition Agreement.

      The closing of this offering is not conditioned on the consummation of the Acquisition. Therefore, upon the closing of this offering, you will become a holder of NRG’s common stock irrespective of whether the Acquisition is consummated or delayed. If the Acquisition is not completed, NRG’s common stock that you have purchased in this offering, will not reflect any interest in Texas Genco, and if the Acquisition is delayed, this interest will not be reflected during the period of delay. If this offering is consummated and the Acquisition does not occur, your expected earnings per share of our common stock will be significantly reduced. Also, the price of NRG’s common stock may decline to the extent that the current market price of NRG’s common stock reflects a market assumption that the Acquisition will be consummated and that NRG will realize certain anticipated benefits of the Acquisition. See also below “—The price of our common stock may fluctuate significantly, which may make it difficult for you to resell the common stock when you want or at prices you find attractive.” In addition, NRG’s business may be harmed to the extent that customers, suppliers and others believe that NRG cannot effectively compete in the marketplace without Texas Genco, or otherwise remain uncertain about NRG. NRG will be required to pay significant costs incurred in connection with the Acquisition, including legal, accounting, financial advisory and other costs, whether or not the Acquisition is completed. The occurrence of any of these events individually or in combination could have a material adverse effect on NRG’s business, financial condition and results of operations.

      The price of our common stock on the New York Stock Exchange constantly changes. We expect that the market price of our common stock will continue to fluctuate. Holders of our common stock will be subject to the risk of volatility and depressed prices.

      Our common stock price can fluctuate as a result of a variety of factors, many of which are beyond our control. These factors include:

      In addition, the stock market in general has experienced extreme volatility that has often been unrelated to the operating performance of a particular company. These broad market fluctuations may adversely affect the market price of our common stock.

      The terms of our existing senior secured credit facility and the indenture for the Second Priority Notes restrict, and we expect the terms of our new senior credit facility and the indenture governing the New Senior Notes to restrict, our ability to pay dividends to the holders of our common stock. In addition, under the terms of our outstanding preferred stock, including the mandatory convertible preferred stock offered as part of the Financing Transactions, we are restricted from paying any cash dividend on our common stock if we are not current in our dividend payments with respect to such preferred stock. If we issue Cumulative Redeemable Preferred Stock to the Sellers pursuant to the Acquisition Agreement, we will be prohibited from paying dividends on our common stock so long as any shares of Cumulative Redeemable Preferred Stock are outstanding. In the future, we may agree to further restrictions on our ability to pay dividends. In addition, to maintain our credit ratings, we may be limited in our ability to pay dividends so that we can maintain an appropriate level of debt. Our future dividend policy depends on earnings, financial condition, liquidity, capital requirements and other factors. There is no guarantee that we will pay dividends on shares of our common stock.

      The offering of the common stock forms part of a larger financing plan for the Acquisition described elsewhere in this prospectus supplement. See “The Acquisition— The Financing Transactions.” Concurrently with this offering, NRG intends to conduct offerings of its mandatory convertible preferred stock and New Senior Notes. In addition, NRG intends to enter into a new senior secured credit facility at or prior to the Acquisition that will replace its existing senior secured credit facility. NRG intends to use initial borrowings under its new senior secured credit facility, together with the net proceeds from this offering and the offerings of mandatory convertible preferred stock and New Senior Notes, to finance the Acquisition and to repay certain of its and Texas Genco’s outstanding indebtedness. See “Use of Proceeds.” NRG’s obligations under the Acquisition Agreement are not conditioned upon the consummation of any or all of the Financing Transactions. NRG has entered into the commitment letter with the bridge lenders pursuant to which the bridge lenders have committed to fund NRG’s new senior secured credit facility and to provide, subject to certain conditions, the additional financing required for the Acquisition through a $5.1 billion bridge loan facility in the event that sufficient proceeds are not raised from this offering, the mandatory convertible

preferred stock offering and/or the New Senior Notes offering. See “Description of Certain Indebtedness— Bridge Loan Facility.”

      In the event that NRG is unable to raise sufficient proceeds through the consummation of the New Senior Notes offering and/or the mandatory convertible preferred stock offering, NRG may draw down on the bridge loan facility, in whole or in part, in order to finance the Acquisition. No assurances can be given that the terms of the bridge loan facility on the draw down date would not vary from the existing terms of such facility on the date of this prospectus supplement. See “Description of Certain Indebtedness— Bridge Loan Facility.” In the event of such draw down, we would be significantly more highly leveraged, which means we will have a larger amount of indebtedness in relation to our equity (deficit). Our interest expense would significantly increase and require us to dedicate a substantial portion of our cash flow from operations to payments in respect of our outstanding indebtedness, thereby reducing the availability of our cash flow to fund working capital, including collateral postings, capital expenditures and other general corporate expenditures. Our substantial indebtedness could adversely affect our financial condition.

      In the event that NRG does not consummate the mandatory convertible stock offering and the New Senior Notes offering as currently contemplated and elects not to consummate the financing under the bridge loan facility, it could seek alternative sources of financing for the Acquisition, which may include, among other alternatives, the issuance in part of senior secured debt securities or borrowing in part on a senior secured basis. This could further exacerbate the risks associated with our substantial leverage. There can be no assurance as to the terms on which NRG would issue these senior secured debt securities or borrow funds. We are unable to predict the interest rate payable on any such debt or give any assurance that the terms would not restrict our financial flexibility or limit our ability to operate our business.

      Provisions in our amended and restated certificate of incorporation and amended and restated by-laws may discourage, delay or prevent a merger or acquisition involving us that our stockholders may consider favorable. For example, our amended and restated certificate of incorporation authorizes our board of directors to issue shares of preferred stock to which special rights are attached, including voting and dividend rights. With these rights, preferred stockholders could make it more difficult for a third party to acquire us. In addition, our amended and restated certificate of incorporation provides for a staggered board of directors, whereby directors serve for three-year terms, with approximately one third of the directors coming up for reelection each year. Having a staggered board of directors would make it more difficult for a third party to obtain control of our board of directors through a proxy contest, which may be a necessary step in an acquisition of us that is not favored by our board of directors.

      We are also subject to the anti-takeover provisions of Section 203 of the Delaware General Corporation Law. Under these provisions, if anyone becomes an “interested stockholder,” we may not enter into a “business combination” with that person for three years without special approval, which could discourage a third party from making a takeover offer and could delay or prevent a change of control. For purposes of Section 203, “interested stockholder” means, generally, someone owning 15% or more of our outstanding voting stock or an affiliate of ours that owned 15% or more of our outstanding voting stock during the past three years, subject to certain exceptions as described in Section 203.

      Under our existing senior secured credit facility and the new senior secured credit facility which we expect will be in effect after closing the Acquisition, a change of control is an event of default. Upon the occurrence of a change in control, the holders of the New Senior Notes will have the right, subject to certain conditions, to require us to repurchase their notes at a price equal to 101% of their principal amount plus accrued and unpaid interest and liquidated damages, if any, to the date of repurchase.

      Issuances or sales of substantial numbers of additional shares of our common stock, including in connection with future acquisitions, if any, or the perception that such issuances or sales could occur, may cause prevailing market prices for shares of our common stock to decline and may adversely affect our ability to raise additional capital in the financial markets at a time and price favorable to us. As of the date of this prospectus supplement, our amended and restated certificate of incorporation provides that we have authority to issue up to 500,000,000 shares of our common stock. As of January 3, 2006, 100,048,676 shares of our common stock were issued, 80,701,888 shares of our common stock were outstanding and 19,346,788 shares of our common stock were issued and held in treasury. Also as of such date, there were 4,000,000 shares of our common stock reserved for issuance under stock incentive plans or pursuant to individual option grants or stock awards. After giving effect to the Financing Transactions, we will have            million shares of common stock outstanding (           million shares of common stock outstanding if the underwriters in this offering exercise their over-allotment option in full).

      In connection with the Acquisition, we are issuing to the Sellers shares of our common stock valued at approximately 1.6 billion on a pro forma basis. The shares of common stock issued to the Sellers are subject to a 180 day lock-up period following the closing date of the Acquisition. If the restrictions under the lock-up agreements are waived or terminated, or upon expiration of the lock-up period, such shares held by the Sellers will be available for sale into the market at that time, subject only to applicable securities laws, rules and regulations. These sales or a perception that these sales may occur could reduce the market price for our common stock.

      Concurrently with this offering, we are offering to sell to the public 2,000,000 shares of our mandatory convertible preferred stock (or 2,300,000 shares if the underwriters exercise their over-allotment option to purchase additional shares in full) and an additional           to            shares of common stock will be issuable upon conversion of the mandatory convertible preferred stock (or an additional           to            shares of common stock if the underwriters exercise their over-allotment option in full). We will reserve for issuance the maximum number of shares of our common stock issuable upon conversion of the mandatory convertible preferred stock. See “Description of Capital Stock— Mandatory Convertible Preferred Stock.”

THE ACQUISITION

The Acquisition

      On September 30, 2005, NRG entered into the Acquisition Agreement with Texas Genco and the Sellers. Pursuant to the Acquisition Agreement, NRG agreed to purchase all of the outstanding equity interests in Texas Genco for a total pro forma purchase price of approximately $6.121 billion that includes the assumption of approximately $2.7 billion of indebtedness. The purchase price is subject to adjustment, and includes an equity component valued at up to $2.0 billion based on a price per share of $45.37 of NRG’s common stock issued to the Sellers, and an average price per share of $40.73 for the preferred stock issued to the Sellers. As a result of the Acquisition, Texas Genco will become a wholly-owned subsidiary of NRG.

      The closing of this offering is not conditioned on the consummation of the Acquisition. While we expect that the Acquisition will be consummated in or about the first week of February 2006, no assurance can be given that the Acquisition will be completed in accordance with the anticipated timing or at all. See “Risk Factors— Risks Related to the Offering— There can be no assurance that the Acquisition will be consummated in accordance with the anticipated timing or at all, and the closing of this offering is not conditioned on the consummation of the Acquisition. If the Acquisition is not consummated, NRG’s common stock will not reflect any actual or anticipated interest in Texas Genco, and if the Acquisition is delayed, this interest will not be reflected during the period of delay.”

      Of the approximately $6.121 billion payable to the Sellers upon consummation of the Acquisition, NRG will pay $4.031 billion in cash, subject to adjustment, and issue a minimum of 35,406,320 shares of NRG’s common stock. The remaining consideration is to be comprised of an additional 9,038,125 shares of common stock, or at NRG’s election, the equivalent in the form of common stock, additional cash or shares of a new series of NRG’s Cumulative Redeemable Preferred Stock, referred to as the Cumulative Preferred Stock, or any combination of the foregoing. If issued, the aggregate liquidation preference of the Cumulative Preferred Stock will be determined by reference to the average price of NRG’s common stock over a 20 trading day period prior to the closing of the Acquisition, which on a pro forma basis is $40.73. If NRG elects to pay all or a portion of the remaining purchase price in cash, the amount payable in cash would be calculated in the same manner. The purchase price payable by NRG is subject to adjustment based on the level of Texas Genco’s working capital, the amount of Texas Genco’s indebtedness and the amount of Texas Genco’s cash and cash equivalents on hand, all as of the closing date.

      The Acquisition Agreement contains customary terms and conditions, including representations and warranties of NRG, Texas Genco and the Sellers and covenants of NRG and Texas Genco with respect to the conduct of their businesses prior to the closing of the Acquisition. Pending closing of the Acquisition, Texas Genco and NRG are obligated to conduct their businesses in the ordinary course of business, to preserve their business, assets, properties and relationships, and to refrain from certain activities without prior written consent of the other party, such consent not to be unreasonably withheld or delayed.

      The obligations of NRG, on the one hand, and Texas Genco and the Sellers, on the other, to consummate the Acquisition are subject to the satisfaction or waiver of various conditions, including: the other party or parties having performed their agreements, covenants and obligations required by the Acquisition Agreement in all material respects and having delivered certain certificates and other documents, the representations and warranties of the other party or parties being true and correct on the date of the Acquisition Agreement and the closing date (except for inaccuracies that would not, individually or in the aggregate, have a Material Adverse Effect (as defined in the Acquisition Agreement)), no Law or Order (each as defined in the Acquisition Agreement) being in effect on the closing date that would prohibit the consummation of the acquisition or related transactions, no Material Adverse Effect on the other party having occurred since June 30, 2005, the parties having received all consents and approvals of, and made all filings with various governmental authorities necessary to consummate the acquisition and related transactions, including with

respect to the NRC and FERC, and any applicable terminations or expirations of waiting periods having occurred, including with respect to the Hart Scott Rodino Antitrust Improvements Act, or the HSRA. On November 10, 2005, NRG was notified by the Federal Trade Commission’s Premerger Notification Office that early termination of the applicable waiting period under the HSRA was granted with respect to the Acquisition. On December 27, 2005, FERC granted approval for the Acquisition. The Acquisition Agreement does not contain any financing condition.

      The Acquisition Agreement may be terminated upon the occurrence of certain events, including at any time before closing by mutual written agreement of NRG and the Seller Representatives (as defined in the Acquisition Agreement). NRG or the Seller Representatives may terminate the Acquisition Agreement if the Acquisition has not been consummated within nine months of the date of the Acquisition Agreement (subject to certain provisions for extension), upon an uncured material breach by the other party or parties of any of the covenants, agreements or representations or warranties in the Acquisition Agreement if such breach would cause a failure of any of the conditions to the obligations of NRG or the Sellers, as the case may be, to consummate the Acquisition, upon an Order by a Governmental Authority (each as defined in the Acquisition Agreement) preventing the consummation of the Acquisition or the related transactions or the failure by a Governmental Authority to issue certain required approvals for the Acquisition or related transactions, which failure becomes final and non-appealable, or if the other party has incurred a Material Adverse Effect (as defined in the Acquisition Agreement) on the other party.

The Financing Transactions

      The offering of common stock forms part of a larger financing plan for the Acquisition described elsewhere in this prospectus supplement. Concurrently with this offering, NRG intends to offer, by means of separate prospectus supplements (i) $500 million of its mandatory convertible preferred stock and (ii) $3.6 billion of New Senior Notes. See “Description of Capital Stock— Mandatory Convertible Preferred Stock” and “Description of Certain Indebtedness—New Senior Notes.” This offering, the mandatory convertible preferred stock offering and the New Senior Notes offering are expected to be consummated at or prior to the completion of the Acquisition. The closing of this offering will not necessarily be contemporaneous with the closing of the New Senior Notes offering and/or the closing of the mandatory convertible preferred stock offering. The net proceeds of the offering of the New Senior Notes (after payment of underwriting discounts and commissions) will be placed into an escrow account held by the escrow agent until the consummation of the Acquisition.

      In addition, NRG intends to enter into a new senior secured credit facility at or prior to the closing of the Acquisition that will replace its existing senior secured credit facility. See “Description of Certain Indebtedness— New Senior Secured Credit Facility.” Concurrently with this offering, NRG is conducting a cash tender offer and consent solicitation with respect to (i) all of its outstanding Second Priority Notes, and (ii) all of Texas Genco’s outstanding Unsecured Senior Notes. The completion of the Acquisition is not conditioned on the completion of the tender offer or receipt of the consents for either the Second Priority Notes or Texas Genco’s Unsecured Senior Notes. The completion of the tender offer for the Second Priority Notes and Texas Genco’s Unsecured Senior Notes is conditioned on the completion of the Acquisition. However, NRG can waive this condition in the case of the tender offer and consent solicitation for the Second Priority Notes. See “Summary— Recent Developments— Tender Offers and Consent Solicitations.”

      NRG intends to use initial borrowings under its new senior secured credit facility, together with the net proceeds from this offering, the offerings of mandatory convertible preferred stock and New Senior Notes and cash on hand (i) to finance the Acquisition, (ii) to repurchase NRG’s outstanding Second Priority Notes, (iii) to repurchase Texas Genco’s outstanding Unsecured Senior Notes, (iv) to repay amounts outstanding under NRG’s existing senior secured credit facility and Texas Genco’s existing senior secured credit facility, (v) for ongoing credit needs of the combined company, including replacement of existing letters of credit and (vi) to pay related premiums, fees and expenses. In the event that NRG does not consummate the Acquisition, NRG intends to use the net proceeds from this offering for general corporate purposes. See “Use of Proceeds.”

      The closing of this offering is not contingent on the closing of the mandatory convertible preferred stock offering, the closing of the New Senior Notes offering, the effectiveness of the new senior secured credit facility, the completion of the tender offers and receipt of the consents in connection with the outstanding tender offers for NRG’s and Texas Genco’s notes or the consummation of the Acquisition. See “Risk Factors— Risks Related to the Offering— There can be no assurance that the Acquisition will be consummated in accordance with the anticipated timing or at all, and the closing of this offering is not conditioned on the consummation of the Acquisition. If the Acquisition is not consummated, NRG’s common stock will not reflect any actual or anticipated interest in Texas Genco, and if the Acquisition is delayed, this interest will not be reflected during the period of delay.” NRG’s obligations under the Acquisition Agreement are not conditioned upon the consummation of any or all of the Financing Transactions.

      NRG has entered into the commitment letter with the bridge lenders pursuant to which the bridge lenders have committed to fund NRG’s new senior secured credit facility and to provide, subject to certain conditions, the additional financing required for the Acquisition through a $5.1 billion bridge loan facility in the event that sufficient funds are not raised from this offering, the mandatory convertible preferred stock and/or the New Senior Notes offering. See “Description of Certain Indebtedness— Bridge Loan Facility.” In the event that NRG is unable to raise sufficient proceeds through the consummation of this offering, the mandatory convertible preferred stock offering and/or the New Senior Notes offering, NRG may draw down on the bridge loan facility, in whole or in part, in order to finance the Acquisition. In the event that NRG does not consummate the mandatory convertible preferred stock offering and the New Senior Notes offering as currently contemplated and elects not to consummate the financing under the bridge loan facility, it could seek alternative sources of financing for the Acquisition, which may include, among other alternatives, the issuance in part of senior secured debt securities or borrowing in part on a senior secured basis.

USE OF PROCEEDS

      We estimate that the net proceeds of this offering, after giving effect to underwriting discounts, commissions and estimated expenses payable by us, will be approximately $                    million. We intend to use the net proceeds from the common stock offering and the offerings of mandatory convertible preferred stock and New Senior Notes, together with initial borrowings under our new senior secured credit facility and cash on hand, (i) to finance the Acquisition, (ii) to repurchase NRG’s outstanding Second Priority Notes, (iii) to repurchase Texas Genco’s outstanding Unsecured Senior Notes, (iv) to repay amounts outstanding under NRG’s existing senior secured credit facility and Texas Genco’s existing senior secured credit facility, (v) for ongoing credit needs of the combined company, including replacement of existing letters of credit and (vi) to pay related premiums, fees and expenses. In the event that NRG does not consummate the Acquisition, NRG intends to use net proceeds from this offering for general corporate purposes. The closing of this offering is not conditioned on the consummation of the Acquisition.

      NRG has agreed to acquire Texas Genco for a total pro forma purchase price of approximately $6.121 billion, including an equity component valued at approximately $2.0 billion. In addition, NRG will assume approximately $2.7 billion of Texas Genco’s debt. Before giving effect to the Acquisition and Financing Transactions, as of September 30, 2005, NRG had (i) $1.08 billion of Second Priority Notes outstanding, which provide for cash interest at 8.0% per annum payable semi-annually and (ii) $876.6 million of outstanding indebtedness under its amended and restated credit facility, which consisted of (a) $446.6 million in term loans outstanding, which term loans provide for interest at a rate of LIBOR (4.02% at September 30, 2005) plus 187.5 basis points payable quarterly and mature on December 24, 2011, (b) $80.0 million in principal amount outstanding under the revolving credit facility, which provides for interest at a rate of LIBOR (3.83% at September 30, 2005) plus 2.5% and matures on December 24, 2007 and (c) $350.0 million outstanding under the funded letter of credit facility, which provide for a participation fee of 1.875%, a deposit fee of 0.10%, and an issuance fee of 0.25% and matures on December 24, 2011. In addition, before giving effect to the Acquisition and Financing Transactions, as of September 30, 2005 (i) Texas Genco had $1.125 billion of Unsecured Senior Notes outstanding, which provide for cash interest at 6.875% per annum payable semiannually and (ii) Texas Genco had $1,614 million in term loans outstanding under its existing senior secured credit facility, which term loans provide for interest at a rate of 5.94% (as of September 30, 2005) payable at least quarterly and mature in December 2011. See “The Acquisition” and “Description of Certain Indebtedness.”

Sources and Uses of Funds

      The following table sets forth the expected sources and uses of funds in connection with the Acquisition on a pro forma basis giving effect to the Transactions as if they had occurred on September 30, 2005. No assurances can be given that the information in the following table will not change depending on the nature of our financings and/or whether the Acquisition will be consummated in accordance with the anticipated timing or at all. See “Risk Factors—Risks Related to the Acquisition—Because the historical and pro forma financial information incorporated by reference or included elsewhere in this prospectus supplement may not be representative of our results as a combined company or capital structure after the Acquisition, and NRG’s and Texas Genco’s historical financial information are not comparable to their current financial information, you have limited financial information on which to evaluate us, NRG, Texas Genco and your investment decision” and “Risk Factors—Risks Related to the Offering—If NRG is unable to raise sufficient proceeds through other Financing Transactions described elsewhere in this prospectus supplement, NRG may draw down on a bridge loan facility in order to close the Acquisition which would significantly increase our indebtedness. If NRG elects not to consummate the financing under the bridge loan facility, NRG may seek alternative sources of financing for the Acquisition, the terms of which are unknown to us and could limit our ability to operate our business” and “Risk Factors—Risks Related to the Offering—There can be no assurance that the Acquisition will be consummated in accordance with the anticipated timing or at all, and the closing of this offering is not conditioned on the consummation of the Acquisition. If the Acquisition is not

consummated, NRG’s common stock will not reflect any actual or anticipated interest in Texas Genco, and if the Acquisition is delayed, this interest will not be reflected during the period of delay.”

CAPITALIZATION

      The following table sets forth NRG’s consolidated capitalization as of September 30, 2005 on an actual historical basis and on a combined pro forma cumulative as adjusted basis to reflect the (i) sale of Audrain; (ii) the refinancing of NRG’s debt structure; (iii) the remaining Financing Transactions and subsequent Acquisition; and (iv) the acquisition of the remaining 50% ownership interest in WCP Holdings and sale of our 50% ownership interest in Rocky Road, as if these transactions were consummated on September 30, 2005. The table below should be read in conjunction with “The Acquisition,” “Use of Proceeds” and the consolidated financial statements and the related notes thereto included in or incorporated by reference into this prospectus supplement and the accompanying prospectus. No assurances can be given that the information in the following table will not change depending on the nature of our financings. See “Risk Factors— Risks Related to the Acquisition— Because the historical and pro forma financial information incorporated by reference or included elsewhere in this prospectus supplement may not be representative of our results as a combined company or capital structure after the Acquisition, and NRG’s and Texas Genco’s historical financial information are not comparable to their current financial information, you have limited financial information on which to evaluate us, NRG, Texas Genco and your investment decision” and “Risk Factors— Risks Related to the Offering— If NRG is unable to raise sufficient proceeds through other Financing Transactions described elsewhere in this prospectus supplement, NRG may draw down on a bridge loan facility in order to close the Acquisition which would significantly increase our indebtedness. If NRG elects not to consummate the financing under the bridge loan facility, NRG may seek alternative sources of financing for the Acquisition, the terms of which are unknown to us and could limit our ability to operate our business” elsewhere in this prospectus supplement. In addition, no assurance can be given that the Acquisition will be consummated in accordance with the anticipated or timing or at all. See “Risk Factors— Risks Related to the Offering— There can be no assurance that the Acquisition will be consummated in accordance with the anticipated timing or at all, and the closing of this offering is not conditioned on the consummation of the Acquisition. If the Acquisition is not consummated, NRG’s common stock will not reflect any actual or anticipated interest in Texas Genco, and if the Acquisition is delayed, this interest will not be reflected during the period of delay.”

PRICE RANGE OF COMMON STOCK AND DIVIDEND POLICY

      Pursuant to the consummation of the NRG plan of reorganization, on December 5, 2003, all shares of our old common stock were canceled and shares of NRG’s new common stock were distributed to the holders of certain classes of claims. From December 5, 2003 to March 24, 2004, NRG’s common stock was listed on the OTC Bulletin Board under the symbol “NRGE.OB.” Since March 25, 2004, NRG’s common stock has been listed for trading on the New York Stock Exchange under the symbol “NRG.” The following table sets forth the quarterly high and low share price information for the periods indicated.

      On January 3, 2006, the closing sale price of NRG’s common stock was $47.95. NRG has not declared or paid dividends on its new common stock, although we may do so in the future. The terms of our existing senior secured credit facility and the indenture for the Second Priority Notes restrict, and we expect the terms of our new senior credit facility and the indenture governing the New Senior Notes to restrict, our ability to pay dividends to the holders of our common stock. See “Description of Certain Indebtedness— New Senior Secured Credit Facility” and “Description of Certain Indebtedness— New Senior Notes.” In addition, under the terms of our outstanding preferred stock, including the mandatory convertible preferred stock offered as part of the Financing Transactions, we are restricted from paying any cash dividend on our common stock if we are not current in our dividend payments with respect to such preferred stock. If we issue Cumulative Redeemable Preferred Stock to the Sellers pursuant to the Acquisition Agreement, we will be prohibited from paying dividends on our common stock so long as any shares of Cumulative Redeemable Preferred Stock are outstanding. See “Description of Capital Stock— Preferred Stock.”

SELECTED CONSOLIDATED FINANCIAL INFORMATION OF NRG

      The following table presents selected historical consolidated financial information of (i) Predecessor Company as of and for the years ended December 31, 2000, 2001 and 2002 and for the period from January 1, 2003 to December 5, 2003 and (ii) Reorganized NRG for the period from December 6, 2003 to December 31, 2003, as of December 31, 2003, as of and for the year ended December 31, 2004 and the nine months ended September 30, 2005 and 2004. “Predecessor Company” refers to NRG’s operations prior to December 6, 2003, before emergence from bankruptcy and “Reorganized NRG” refers to NRG’s operations from December 6, 2003 onwards, after emergence from bankruptcy.

      The selected historical consolidated financial information of Predecessor Company as of and for the year ended December 31, 2000, 2001 and 2002 and for the period from January 1, 2003 to December 5, 2003 is derived from the historical financial information contained in the audited consolidated financial statements of Predecessor Company incorporated by reference in this prospectus supplement.

      The selected historical consolidated financial information of Reorganized NRG for the period December 6, 2003 to December 31, 2003 and as of and for the year ended December 31, 2004 is derived from the historical financial information contained in the audited consolidated financial statements of Reorganized NRG incorporated by reference in this prospectus supplement. The summary unaudited historical consolidated financial information as of and for the nine months ended September 30, 2005 and 2004 (i) have been derived from Reorganized NRG’s unaudited consolidated financial statements which are incorporated by reference in this prospectus supplement, (ii) have been prepared on a similar basis to that used in the preparation of the audited financial statements of Reorganized NRG and (iii) in the opinion of NRG’s management, include all adjustments necessary for a fair statement of the results for the unaudited interim period.

      The selected historical consolidated financial information set forth below should be read in conjunction with management’s discussion and analysis of financial condition and results of operations and the consolidated financial statements of Predecessor Company and Reorganized NRG and the related notes thereto incorporated by reference into this prospectus supplement. The results for period of less than a full year are not necessarily indicative of the results to be expected for any interim period.

SELECTED CONSOLIDATED FINANCIAL INFORMATION OF TEXAS GENCO

      The following table sets forth selected historical consolidated financial information for Texas Genco LLC and its subsidiaries and for Texas Genco Holdings, Inc., Texas Genco LLC’s predecessor for financial reporting purposes, and its subsidiaries. Because Texas Genco LLC acquired Texas Genco Holdings, Inc. as part of a multi-step transaction in which the Initial Acquisition (as described below) was consummated on December 15, 2004 and the Nuclear Acquisition (as described below) was consummated on April 13, 2005, information is presented for (i) Texas Genco Holdings, Inc. as of and for the years ended December 31, 2002, 2003 and 2004, and as of and for the nine months ended September 30, 2004 and for the period from January 1, 2005 through April 13, 2005 and (ii) Texas Genco LLC as of December 31, 2004, the period from July 19, 2004, or Inception, through December 31, 2004 and as of and for the nine months ended September 30, 2005.

      The selected historical consolidated financial information for Texas Genco Holdings, Inc. as of and for the years ended December 31, 2000, 2001, 2002, 2003 and 2004 were derived from Texas Genco Holdings, Inc.’s audited financial statements incorporated by reference into this prospectus supplement. The selected historical consolidated financial information for Texas Genco Holdings, Inc. as of and for the nine months ended September 30, 2004 and for the period from January 1, 2005 through April 13, 2005 (i) were derived from Texas Genco Holdings, Inc.’s unaudited financial statements, (ii) have been prepared on a similar basis to that used in the preparation of Texas Genco Holdings, Inc.’s audited financial statements, and (iii) in the opinion of Texas Genco’s management, include all adjustments necessary for a fair statement of the results for the unaudited interim period. The financial information for Texas Genco Holdings, Inc. reflects ownership of the Non-Nuclear Assets for periods prior to December 15, 2004 and of an undivided 44.0% interest in STP for all periods presented, and is therefore not comparable to the historical financial information for Texas Genco LLC, which reflects ownership of the Non-Nuclear Assets only for periods subsequent to December 15, 2004, the Nuclear Acquisition only for periods subsequent to April 13, 2005 and the ROFR (as described below) only for periods subsequent to May 19, 2005.

      The selected historical consolidated financial information for Texas Genco LLC as of December 31, 2004 and for the period from July 19, 2004 (Inception) through December 31, 2004 were derived from the audited consolidated financial statements of Texas Genco LLC incorporated by reference into this prospectus supplement. The selected historical consolidated financial information for Texas Genco LLC as of and for the nine months ended September 30, 2005 (i) were derived from unaudited financial statements of Texas Genco LLC incorporated by reference into this prospectus supplement, (ii) have been prepared on a similar basis to that used in the preparation of the audited financial statements of Texas Genco LLC, and (iii) in the opinion of Texas Genco’s management, include all adjustments necessary for a fair statement of the results for the unaudited interim period. The results for a periods for less than a full year are not necessarily indicative of the results to be expected for any interim period. Texas Genco LLC did not exist prior to Inception; therefore, no consolidated financial and other information has been presented in the following table for Texas Genco LLC for any other period.

      The selected consolidated historical financial information of Texas Genco LLC and Texas Genco Holdings, Inc. set forth below should be read in conjunction with management’s discussion and analysis of financial condition and results of operations and the consolidated financial statements of Texas Genco LLC and Texas Genco Holdings, Inc. and the related notes thereto incorporated by reference into this prospectus supplement.