The Company's net ownership interests in estimated quantities of proved oil and natural gas reserves and changes in net proved reserves, all of which are located in the continental United States, are summarized below:

The Company uses the cost method of accounting to record its investment in Pinnacle, formed in June 2003. Accordingly, the proved reserve tables, above, do not include the Company’s interest ownership, approximately 8.3% of the shares on a fully diluted basis, in Pinnacle at the end of 2007.

During 2007, 2006 and 2005, the Company reported considerable discoveries and extensions to the Company’s natural gas reserves primarily due to the Company’s drilling program in the Barnett Shale play. In 2007, the Company recorded significant oil discoveries and extensions due to drilling and development activity in the Barnett Shale region and additional formation evaluation in the Camp Hill field. In 2007, the Company reported a large natural gas revision largely attributable to the reclass of natural gas liquids, previously presented as natural gas equivalents, to the reserve category of oil and condensate. During 2007, the Company increased production of natural gas liquids as a result of an increase in processed gas sales. In prior years, anynatural gas liquid production was deemed immaterial. The Company reported significant downward revisions to its natural gas reserves in 2006 and 2005 due to a decline in natural gas prices and additional information from seismic data in the Barnett Shale play in 2005. In 2005, the Company incurred a significant downward revision in its oil reserves mainly due to a reduction in theanticipated overall recovery efficiency factor in the Camp Hill field.