Estimated proved reserves increased 86 percent to 26.2 billion cubic feet equivalent ( " Bcfe " ) as of December 31 , 2008 , compared to 14.1 Bcfe on December 31 , 2007 . Proved reserves consisted of 18.1 Bcfe of proved developed reserves and 8.1 Bcfe of proved undeveloped reserves . Proved reserves were 64 percent natural gas and 36 percent crude oil .