Exhibit 5

JOINT FILING AGREEMENT

Dated as of August 11, 2006

In accordance with Rule 13d-1(k) promulgated under the Securities Exchange Act of 1934, as amended, each of the undersigned hereby agrees to the joint filing on behalf of each of the undersigned of Amendment No. 1 to the Schedules 13D filed by the undersigned on February 10, 2006 (including any and all amendments to such Amendment No. 1) with respect to the shares of common stock, par value $0.01 per share, of NRG Energy, Inc., a Delaware corporation, and that this Joint Filing Agreement may be included as an Exhibit to such joint filing.

Each of the undersigned agrees that each party hereto is responsible for the timely filing of such Amendment No. 1 (including any and all amendments thereto) and for the completeness and accuracy of the information concerning such party contained therein, provided that no party is responsible for the completeness and accuracy of the information concerning any other party, unless such party actually knows that such information is incorrect.  Each party will indemnify the other parties for any incompleteness or inaccuracy in such information concerning the indemnifying party.

This Joint Filing Agreement may be executed in any number of counterparts, all of which together shall constitute one and the same instrument.

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IN WITNESS WHEREOF, the undersigned hereby execute this Joint Filing Agreement as of the date first written above.

BLACKSTONE TG CAPITAL PARTNERS IV L.P.
By:	Blackstone Management Associates IV L.L.C., as General
	Partner
By:	/s/ David Foley
	Name:	David Foley
	Title:	Member
BLACKSTONE TG CAPITAL PARTNERS IV-B L.P.
By:	Blackstone Management Associates IV L.L.C., as General
	Partner
By:	/s/ David Foley
	Name:	David Foley
	Title:	Member
BLACKSTONE CAPITAL PARTNERS IV-A L.P.
By:	Blackstone Management Associates IV L.L.C., as General
	Partner
By:	/s/ David Foley
	Name:	David Foley
	Title:	Member
BLACKSTONE PARTICIPATION PARTNERSHIP IV L.P.
By:	Blackstone Management Associates IV L.L.C., as General
	Partner
By:	/s/ David Foley
	Name:	David Foley
	Title:	Member
BLACKSTONE FAMILY INVESTMENT PARTNERSHIP IV- A L.P.
By:	Blackstone Management Associates IV L.L.C., as General
	Partner
By:	/s/ David Foley
	Name:	David Foley
	Title:	Member

2

BLACKSTONE MANAGEMENT ASSOCIATES IV L.L.C.
By:	/s/ David Foley
	Name:	David Foley
	Title:	Member
/s/ Peter G. Peterson
PETER G. PETERSON
/s/ Stephen A. Schwarzman
STEPHEN A. SCHWARZMAN

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HELLMAN & FRIEDMAN CAPITAL PARTNERS IV, L.P.
By:	H&F Investors IV, LLC, its General Partner
By:	/s/ Georgia Lee
	Georgia Lee, Managing Director
H&F INTERNATIONAL PARTNERS IV-A, L.P.
By:	H&F Investors IV, LLC, its General Partner
By:	/s/ Georgia Lee
	Georgia Lee, Managing Director
H&F INTERNATIONAL PARTNERS IV-C, L.P.
By:	H&F Investors IV, LLC, its General Partner
By:	/s/ Georgia Lee
	Georgia Lee, Managing Director
H&F EXECUTIVE FUND IV, L.P.
By:	H&F Investors IV, LLC, its General Partner
By:	/s/ Georgia Lee
	Georgia Lee, Managing Director
H&F TGN AIV, L.P.
By:	H&F Investors IV, LLC, its General Partner
By:	/s/ Georgia Lee
	Georgia Lee, Managing Director
H&F INVESTORS IV, LLC
By:	/s/ Georgia Lee
	Georgia Lee, Managing Director

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KKR MILLENNIUM FUND (ENERGY) L.P.
By:	KKR Associates Millennium (Energy) L.P., its General
	Partner
By:	KKR Millennium GP (Energy) LLC, its General Partner
By:	/s/ Marc S. Lipschultz
	Name:	Marc S. Lipschultz
	Title:	Member
KKR PARTNERS III, L.P. (SERIES I)
By:	KKR Millennium GP (Energy) LLC, a General Partner
By:	/s/ Marc S. Lipschultz
	Name:	Marc S. Lipschultz
	Title:	Member
KKR ASSOCIATES MILLENNIUM (ENERGY) L.P.
By:	KKR Millennium GP (Energy) LLC, its General Partner
By:	/s/ Marc S. Lipschultz
	Name:	Marc S. Lipschultz
	Title:	Member
KKR MILLENNIUM GP (ENERGY) LLC
By:	/s/ Marc S. Lipschultz
	Name:	Marc S. Lipschultz
	Title:	Member

5

TPG ADVISORS III, INC.
By:	/s/ David A. Spuria
	Name:	David A. Spuria
	Title:	Vice President
TPG ADVISORS IV, INC.
By:	/s/ David A. Spuria
	Name:	David A. Spuria
	Title:	Vice President

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