LEASE AMENDMENT AND EXTENSION AGREEMENT

Exhibit 10.6

LEASE AMENDMENT AND EXTENSION AGREEMENT

This lease amendment and extension agreement is made August 17, 2006, between CALIBER DEVELOPMENT COMPANY LLC (the “Landlord”), and DIAMONDBACK-PUMPING SERVICE, L.P. (the “Tenant”).

WITNESSETH :

WHEREAS, pursuant to the lease dated July 1, 2006 (the “Lease”), Tenant let from Landlord certain real property and improvements situated thereon physically located in Johnson County, Texas, and more particularly described in Exhibit “A” of said Lease, for an initial term of ten (10) years (“Initial Term”).

WHEREAS, the Landlord and Tenant desire to amend the ten (10) year Initial Term of the Lease to twenty (20) years.

NOW, THEREFORE, in consideration of the