Joint Filing Agreement

Exhibit 7.1

Joint Filing Agreement

This will confirm the agreement by and among all the undersigned that the Statement on Schedule 13D filed on or about this date and any further amendments thereto with respect to beneficial ownership by the undersigned of the Common Shares of TransAlta Corporation, a corporation incorporated under the Canada Business Corporations Act, is being filed on behalf of each of the undersigned in accordance with Rule 13d-1(k)(1) under the Securities Exchange Act of 1934.

The undersigned further agree that each party hereto is responsible for timely filing of such Statement on Schedule 13D and any further 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 the other party, unless such party knows or has reason to believe that such information is inaccurate. The undersigned further agree that this Agreement shall be included as an Exhibit to such joint filing.

This agreement may be executed in two or more counterparts, each of which shall be deemed an original, but all of which together shall constitute one and the same instrument.

Dated: July 6, 2007

LSP Penn Holdings, LLC
By:		/s/ Xxxxx Xxxxxxxx
Name:		Xxxxx Xxxxxxxx
Title:		President
LSP Penn Holdings II, LLC
By:		/s/ Xxxxx Xxxxxxxx
Name:		Xxxxx Xxxxxxxx
Title:		President
LS Power Partners, L.P.
By:		/s/ Xxxxx Xxxxxxxx
Name:		Xxxxx Xxxxxxxx
Title:		President
LS Power Partners II, L.P.
By:		/s/ Xxxxx Xxxxxxxx
Name:		Xxxxx Xxxxxxxx
Title:		President
Luminus Management, LLC
By:		/s/ Xxxx Xxxxx
Name:		Xxxx Xxxxx
Title:		President
Luminus Asset Partners, L.P.
By:		/s/ Xxxx Xxxxx
Name:		Xxxx Xxxxx
Title:		President
Luminus Energy Partners Master Fund, Ltd.
By:		/s/ Xxxx Xxxxx
Name:		Xxxx Xxxxx
Title:		Director