SALE OF ARKOMA BASIN
WOODFORD SHALE BLOCK

CONCENTRATED OPERATED PROJECT
PRIMARILY LOCATED IN HUGHES COUNTY, OK
WITH ADDITIONAL ACREAGE IN COAL AND ATOKA COUNTIES, OK

• Over 10,000 net acres of contiguous leasehold in primary area
• Additional 2,200 net acres located throughout active region of the
  trend in Coal and Atoka Counties
• Bulk of acreage located immediately northwest of intense Newfield,
  Devon and Continental drilling activity
• Control of operations with dominant leasehold interests in
  approximately 34 sections
• Active drilling program in place with 150 net potential horizontal
  Woodford locations on 80 acre spacing
• 2008 drilling program is expected to yield >5 MMCFPD net to
  Cornerstone by year-end
• Completed horizontal Woodford well costs of $3.0MM and estimated
  recovery of 2.4 BCF
• Primary target - Woodford Shale, 5,000’ average depth with thickness
  of 150’ to 250’ and favorable thermal maturity
• Numerous proven secondary target zones with cumulative production
  of 352 BCFE within the two primary townships
• Over 70% of leasehold with term that extends beyond mid-2009
• Approximately 79% average net revenue interest
• Extensive land work complete for OCC and drilling purposes
• Proprietary 3D seismic shoot currently in progress over 21 square miles
• 2D seismic available over most of primary acreage block
• One non-operated Woodford horizontal well producing since 12/07
• One operated Woodford horizontal well in completion stage with
  anticipated first gas sales 4/01/08
• Gathering and processing infrastructure in place

WELL LIST

Primary Area: Horizontal Woodford (Drilling, TD’d, or Producing)

Southern Area:  Horizontal Woodford (Drilling, TD’d, or Producing)

Technical Presentation and Data Room open in Meagher’s Tulsa Office March 19, 2008