SUPPLEMENTALGUARANTEE AGREEMENT

Exhibit 10.17

SUPPLEMENTAL GUARANTEE AGREEMENT

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

WITNESSETH

WHEREAS, the Company and the Subsidiary Guarantors have heretofore executed and delivered to the Trustee a Guarantee Agreement (the “Guarantee Agreement”), dated as of December 22, 2004, providing for the Company’s guarantee (the “REI Guarantee”) of the Pennsylvania Economic Development Financing Authority’s (“PEDFA”) Exempt Facilities Revenue Bonds (Reliant Energy Seward, LLC Project), Series 2003A (the “Series 2003A Bonds”), and the Subsidiary Guarantors’ guarantees of the REI Guarantee;

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

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

NOW THEREFORE, in consideration of the foregoing and for good and valuable consideration, the receipt of which is hereby acknowledged, the Guaranteeing Subsidiary, the Trustee, the Company and the other Subsidiary Guarantors mutually covenant and agree for the equal and ratable benefit of the Holders of the Series 2003A Bonds as follows:

1.             Capitalized Terms.  Unless otherwise defined in this Supplemental Guarantee Agreement, capitalized terms used herein without definition shall have the meanings assigned to them in the Guarantee Agreement.

2.             Agreement to be Bound; Guarantee.  The Guaranteeing Subsidiary hereby becomes a party to the Guarantee Agreement as a Subsidiary Guarantor and as such will have all of the rights and be subject to all of the Obligations and agreements of a Subsidiary Guarantor under the Guarantee Agreement.  The Guaranteeing Subsidiary hereby agrees to be bound by all of the provisions of the Guarantee Agreement applicable to a Subsidiary Guarantor and to perform all of the Obligations and agreements of a Subsidiary Guarantor under the Guarantee Agreement.  In furtherance of the foregoing, the Guaranteeing Subsidiary shall be deemed a Subsidiary Guarantor for purposes of Article 12 of the Guarantee Agreement, including, without limitation, Section 12.02 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 TO CONSTRUE THIS SUPPLEMENTAL GUARANTEE AGREEMENT BUT WITHOUT GIVING EFFECT TO APPLICABLE PRINCIPLES OF CONFLICTS OF LAW TO THE EXTENT THAT THE APPLICATION OF THE LAWS OF ANOTHER JURISDICTION WOULD BE REQUIRED THEREBY.