1 EXHIBIT 21 SUBSIDIARIES OF THE REGISTRANT State or Jurisdiction Ownership Name Of Incorporation Percentage ---- --------------------- ---------- Vista Resources I, Inc. Texas 100% Vista LLC Delaware 100% Vista Resources, Inc. Texas 100% Vista Resources Partners, L.P. Texas 100% Midland Resources, Inc. Texas 100% Prize Natural Resources, Inc. Delaware 100% Prize Operating Company Delaware 100% Prize Energy Resources, L.P. Delaware 100% PEC (Delaware), Inc. Delaware 100% Prize Petroleum L.L.C. Delaware 100% Oklahoma Gas Processing, Inc. Delaware 100% Sunterra Petroleum, L.L.C. Delaware 100%