**Exhibit 10.15**

**SUPPLEMENTALGUARANTEE AGREEMENT**

Supplemental GuaranteeAgreement (this “*Supplemental GuaranteeAgreement*”), dated as of September 21, 2006, among ReliantEnergy Power Supply, LLC (the “*GuaranteeingSubsidiary*”), a Delaware limited liability company, a subsidiary ofReliant Energy, Inc. (or its permitted successor), a Delaware corporation (the “*Company*”), the Company, the other SubsidiaryGuarantors (as defined in the Guarantee Agreement referred to herein) and J.P.Morgan Trust Company, National Association, as trustee under the Indenture (asdefined in the Guarantee Agreement referred to below) (the “*Trustee*”).

**WITNESSETH**

WHEREAS, the Company and the Subsidiary Guarantors haveheretofore executed and delivered to the Trustee a Guarantee Agreement (the *“Guarantee Agreement”*), dated as of December 22, 2004, providingfor the Company’s guarantee (the *“REI Guarantee”*)of the Pennsylvania Economic Development Financing Authority’s (*“PEDFA”*) Exempt Facilities Revenue Bonds (Reliant EnergySeward, LLC Project), Series 2002A (the *“Series 2002A Bonds”*),and the Subsidiary Guarantors’ guarantees of the REI Guarantee;

WHEREAS, the Guarantee Agreement provides that undercertain circumstances the Guaranteeing Subsidiary shall execute and deliver tothe Trustee a supplemental guarantee agreement pursuant to which theGuaranteeing Subsidiary shall unconditionally guarantee all of the Company’sObligations under the REI Guarantee and the Guarantee Agreement (the “*Subsidiary Guarantee*”); and

WHEREAS, pursuant to Section 9.01 of the GuaranteeAgreement, the Trustee, the Company and the other Subsidiary Guarantors areauthorized to execute and deliver this Supplemental Guarantee Agreement.

NOW THEREFORE, in consideration of the foregoing andfor good and valuable consideration, the receipt of which is herebyacknowledged, the Guaranteeing Subsidiary, the Trustee, the Company and theother Subsidiary Guarantors mutually covenant and agree for the equal andratable benefit of the Holders of the Series 2002A Bonds as follows:

1.             *Capitalized Terms*.  Unless otherwise defined in this SupplementalGuarantee Agreement, capitalized terms used herein without definition shallhave the meanings assigned to them in the Guarantee Agreement.

2.             *Agreement to be Bound;Guarantee*.  The GuaranteeingSubsidiary hereby becomes a party to the Guarantee Agreement as a Subsidiary Guarantorand as such will have all of the rights and be subject to all of theObligations and agreements of a Subsidiary Guarantor under the GuaranteeAgreement.  The Guaranteeing Subsidiaryhereby agrees to be bound by all of the provisions of the Guarantee Agreement applicableto a Subsidiary Guarantor and to perform all of the Obligations and agreementsof a Subsidiary Guarantor under the Guarantee Agreement.  In furtherance of the foregoing, theGuaranteeing Subsidiary shall be deemed a Subsidiary Guarantor for purposes ofArticle 12 of the Guarantee Agreement, including, without limitation, Section12.02 thereof.

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3.             ***NEW YORK LAW TO GOVERN*. THE INTERNAL LAW OF THE STATE OF NEW YORK SHALL GOVERN AND BE USED TOCONSTRUE THIS SUPPLEMENTAL GUARANTEE AGREEMENT BUT WITHOUT GIVING EFFECT TOAPPLICABLE PRINCIPLES OF CONFLICTS OF LAW TO THE EXTENT THAT THE APPLICATION OFTHE LAWS OF ANOTHER JURISDICTION WOULD BE REQUIRED THEREBY.**

4.             *Counterparts*.  The parties may sign any number of copies ofthis Supplemental Guarantee Agreement. Each signed copy shall be an original, but all of them togetherrepresent the same agreement.

5.             *Effect of Headings*.  The Section headings herein are forconvenience only and shall not affect the construction hereof.

6.             *The Trustee*.  The Trustee shall not be responsible in anymanner whatsoever for or in respect of the validity or sufficiency of thisSupplemental Guarantee Agreement or for or in respect of the recitals containedherein, all of which recitals are made solely by the Guaranteeing Subsidiaryand the Company.

7.             *Ratification of GuaranteeAgreement; Supplemental Guarantee Agreement Part of Guarantee Agreement*.  Except as expressly amended hereby, the GuaranteeAgreement is in all respects ratified and confirmed and all the terms,conditions and provisions thereof shall remain in full force and effect.  This Supplemental Guarantee Agreement shallform a part of the Guarantee Agreement for all purposes, and every Holder of Series2002A Bonds heretofore or hereafter authenticated and delivered shall by boundhereby.

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IN WITNESS WHEREOF, the parties hereto have causedthis Supplemental Guarantee Agreement to be duly executed and attested, all asof the date first above written.

Dated : September 21, 2006.
|        |   | RELIANT ENERGY POWER SUPPLY,  LLC |
|--------|--------|-----------------------------------|
|   |   |                              |
|   |   |                              |
|   |   | By:                               | /s/ Lloyd A.  Whittington |
|   |   | Name:                             | Lloyd A.  Whittington |
|   |   | Title:                            |  Vice President and Treasurer |
|   |   |                              |
|   |   | RELIANT ENERGY,  INC.             |
|   |   |                              |
|   |   |                              |
|   |   | By:                               |  /s/ Andrew C. Johannesen |
|   |   | Name:                             |  Andrew C. Johannesen |
|   |   | Title:                            |  Vice President and Asst. Treasurer |
|        |        |                                   |  |  |  |

 

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|        |   |   |   | RELIANT ENERGY ASSET MANAGEMENT, LLC      |
|--------|--------|--------|--------|-------------------------------------------|
|   |   |   |   | RELIANT ENERGY BROADBAND, INC.            |
|   |   |   |   | RELIANT ENERGY CALIFORNIA HOLDINGS, LLC   |
|   |   |   |   | RELIANT ENERGY COMMUNICATIONS, INC.       |
|   |   |   |   | RELIANT ENERGY COOLWATER, INC.            |
|   |   |   |   | RELIANT ENERGY CORPORATE SERVICES, LLC    |
|   |   |   |   | RELIANT ENERGY ELLWOOD, INC.              |
|   |   |   |   | RELIANT ENERGY ETIWANDA, INC.             |
|   |   |   |   | RELIANT ENERGY FLORIDA, LLC               |
|   |   |   |   | RELIANT ENERGY KEY/CON FUELS, LLC         |
|   |   |   |   | RELIANT ENERGY MANDALAY, INC.             |
|   |   |   |   | RELIANT ENERGY NORTHEAST GENERATION, INC. |
|   |   |   |   | RELIANT ENERGY NORTHEAST HOLDINGS, INC.   |
|   |   |   |   | RELIANT ENERGY ORMOND BEACH, INC.         |
|   |   |   |   | RELIANT ENERGY POWER GENERATION, INC.     |
|   |   |   |   | RELIANT ENERGY RETAIL HOLDINGS, LLC       |
|   |   |   |   | RELIANT ENERGY SABINE (TEXAS), INC.       |
|   |   |   |   | RELIANT ENERGY SERVICES DESERT BASIN, LLC |
|   |   |   |   | RELIANT ENERGY SERVICES MID-STREAM, LLC   |
|   |   |   |   | RELIANT ENERGY SEWARD, LLC                |
|   |   |   |   | RELIANT ENERGY TRADING EXCHANGE, INC.     |
|   |   |   |   | RELIANT ENERGY VENTURES, INC.             |
|   |   |   |   | RELIANT ENERGY WHOLESALE GENERATION, LLC  |
|   |   |   |   |                                      |
|   |   |   |   |                                      |
|   |   |   |   | By:                                       | /s/ Andrew C. Johannesen |   |
|   |   |   |   | Name:                                     | Andrew C. Johannesen |
|   |   |   |   | Title:                                    | Assistant Treasurer of the corporations and limited |
|   |   |   |   |                                      | liability companies, and of the general partners of  the limited partnerships, listed above |
|        |        |        |        |                                           |  |  |  |

 

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|        |   | RELIANT ENERGY SERVICES, INC.          |
|--------|--------|----------------------------------------|
|   |   |                                   |
|   |   |                                   |
|   |   | By:                                    | /s/ Andrew C. Johannesen |   |
|   |   | Name:                                  | Andrew C. Johannesen |
|   |   | Title:                            | Vice President and Treasurer |
|   |   |                                   |
|   |   | RELIANT ENERGY RETAIL SERVICES, LLC    |
|   |   | RELIANT ENERGY ELECTRIC SOLUTIONS, LLC |
|   |   | RELIANT ENERGY SOLUTIONS EAST, LLC     |
|   |   |                                   |
|   |   |                                   |
|   |   |                                   |
|   |   | By:                                    | /s/ Lloyd A. Whittington |   |
|   |   | Name:                                  | Lloyd A. Whittington |
|   |   | Title:                                 | Vice President and Treasurer of the limited |
|   |   | liability companies listed above       |
|        |        |                                        |  |  |  |  |  |  |

 

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|   | RELIANT ENERGY CAPTRADES  HOLDING CORP. |
|--------|-----------------------------------------|
|   | RELIANT ENERGY  SABINE (DELAWARE), INC. |
|   |                                    |
|   |                                    |
|   | By:                                     | /s/ Patricia F.  Genzel |
|   | Name:                                   | Patricia F.  Genzel |
|   | Title:                                  | President |
|        |                                         |  |  |  |

 

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|        | J.P. MORGAN TRUST COMPANY, NATIONAL ASSOCIATION, as  Trustee |
|--------|--------------------------------------------------------------|
|   |                                                         |
|   |                                                         |
|   | By:                                                          |  /s/ Michael  J. Judge |   |
|   |                                                         | Authorized  Signatory |   |

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