EXHIBIT 11 MarkWest Hydrocarbon, Inc. Computation of Earnings per Common Share (000s, except per share data) FOR THE THREE MONTHS FOR THE SIX MONTHS ENDED JUNE 30, ENDED JUNE 30, 1997 1996 1997 1996 ------------------------------------------ Net income (a) $ 300 $ 195 $4,582 $2,783 Weighted average common 8,484 7,908 8,484 7,908 shares outstanding (a) Earnings per common share (a) $ 0.04 $ 0.02 $ 0.54 $ 0.35 (a) Pro forma for 1996