AGREEMENT REGARDING THE JOINT FILING OF SCHEDULE 13G

EXHIBIT A

AGREEMENT REGARDING THE JOINT FILING OF SCHEDULE 13G

The undersigned hereby agree as follows:

1.     Each of them is individually eligible to use the Schedule 13G to which this Exhibit is attached, and such Schedule 13G is filed on behalf of each of them; and

2.     Each of them is responsible for the timely filing of such Schedule 13G and any amendments thereto, and for the completeness and accuracy of the information concerning such person contained therein; but none of them is responsible for the completeness or accuracy of the information concerning the other persons making the filing, unless such person knows or has reason to believe that such information is inaccurate.

Date: February 19, 2009

[Signature Pages Follow]

	C/R CDM HOLDINGS II, L.P.
		By:		Carlyle/Riverstone Energy Partners II, L.P.
				Its General Partner
				By: C/R Energy XX XX, LLC
				Its General Partner
		By:		/s/ Xxxxxx X. Xxxxxxx, Xx.
				Name: Xxxxxx X. Xxxxxxx, Xx.
				Title: Authorized Person
	CARLYLE/RIVERSTONE ENERGY
			PARTNERS II, L.P.
		By:		C/R Energy XX XX, LLC
				Its: General Partner
		By:		/s/ Xxxxxx X. Xxxxxxx, Xx.
				Name: Xxxxxx X. Xxxxxxx, Xx.
				Title: Authorized Person
	C/R ENERGY XX XX, LLC
		By:		/s/ Xxxxxx X. Xxxxxxx, Xx.
				Name: Xxxxxx X. Xxxxxxx, Xx.
				Title: Authorized Person

	TC GROUP INVESTMENT HOLDINGS, L.P.
		By:	TCG Holdings II, L.P.
			Its General Partner
			By: DBD Investors V, L.L.C.
			Its General Partner
		By:	/s/ Xxxxxx X. X’Xxxxxxx
			Name:Xxxxxx X. X’Xxxxxxx
			Title: Managing Director
	TCG HOLDINGS II, L.P.
		By:	DBD Investors V, L.L.C.
			Its General Partner
		By:	/s/ Xxxxxx X. X’Xxxxxxx
			Name:Xxxxxx X. X’Xxxxxxx
			Title: Managing Director
	DBD INVESTORS V, L.L.C.
		By:	/s/ Xxxxxx X. X’Xxxxxxx
			Name:Xxxxxx X. X’Xxxxxxx
			Title: Managing Director

	RIVERSTONE INVESTMENT SERVICES LLC
		By:	/s/ Xxxxxx X. Xxxxxx
			Name: Xxxxxx X. Xxxxxx
			Title: Authorized Person
	RIVERSTONE HOLDINGS LLC
		By:	/s/ Xxxxxx X. Xxxxxx
			Name: Xxxxxx X. Xxxxxx
			Title: Authorized Person

	CARLYLE INVESTMENT MANAGEMENT
			L.L.C.
		By:		TC Group, L.L.C.
				Its: Managing Member
		By:		TCG Holdings, L.L.C.
				Its: Managing Member
		By:		/s/ Xxxxxx X. X’Xxxxxxx
				Name:Xxxxxx X. X’Xxxxxxx
				Title: Managing Director
	TCG HOLDINGS, L.L.C.
		By:		/s/ Xxxxxx X. X’Xxxxxxx
				Name:Xxxxxx X. X’Xxxxxxx
				Title: Managing Director
	TC GROUP, L.L.C.
	By:	TCG Holdings, L.L.C.
		Its: Managing Member
		By:		/s/ Xxxxxx X. X’Xxxxxxx
				Name:Xxxxxx X. X’Xxxxxxx
				Title: Managing Director