Pioneer Provides Operational Update

Pioneer has completed drilling operations on three of its four Gulf of Mexico shelf wells scheduled for 2001. Two of the wells are currently being completed and tested while one well was dry. The Stirrup prospect in Mustang Island 861 was drilled to a total depth of 17,123 feet and found multiple gas-bearing sands. Operations are currently underway to test the productivity of the individual sands, and results should be available within the next month. Pioneer has a 25% working interest in the prospect which is operated by Spinnaker Exploration Company with a 42% working interest. Pioneer and partners increased their lease holdings in the area at the July 10 Texas state lease sale adding 2,880 acres in the play.

The Oneida prospect in East Cameron Block 76 was drilled to a total depth of 17,766 feet and found over 50 feet of net gas pay in a single CibOp sand. The well is currently being completed and well test results should be announced shortly. Pioneer has a 13.7% working interst in the well which is operated by Hall-Houston Oil Company with a 20% working interest.

The Pioneer-operated Cruiser prospect in West Cameron 296 was drilled to a total depth of 17,785 feet and encountered over 200 feet of sand in the Lower Miocene target. Although good hydrocarbons shows were encountered in the objective interval, logs indicated porosity and hydrocarbon saturation too low to be commercial. The well is currently being plugged and abandoned, after which the rig will move to Pioneer's Malta prospect to drill an 11,300 feet Marg A test in Mustang Island A-11.

Pioneer is currently drilling on its Argo prospect in Alaminos Canyon 13 where Pioneer is operator with a 75% working interst and Mariner Energy, Inc. holds a 25% working interest. This prospect is located approximately 30 miles southeast of the partners' previously announced Falcon discovery in East Breaks 579. Results from the Argo well are expected within a month.

Pioneer recently completed drilling operations on the E-DQ2 appraisal well to the Boomslang discovery located on the southern rim of the Bredasdorp Basin in the Block 9 area of South Africa. The well was drilled to test a separate fault block within the Boomslang structure approximately two kilometers southwest of the discovery well. The well was drilled to a total depth of 2,472 meters and encountered over 180 meters of high quality sand in the same interval as the discovery well. However, the reservoir sand came in low to the oil-water contact intersected in the Boomslang discovery well and was wet. Pioneer recently acquired a 1,193 square kilometer 3-D seismic survey covering the Boomslang structure and several analogous prospects and plans to continue its drilling program to appraise the Boomslang discovery in 2002 upon completion of development drilling at the Sable field.

Drilling and testing operations have also been completed on the first well on Pioneer's 2.7 million acres in the Ghadames Basin of southern Tunisia. The Douz #1, operated by Eurogas Corporation, was drilled on the Bazma permit to a total depth of 2,317 meters to test a TAGI sand prospect. Over 35 meters of high-quality TAGI sand with strong hydrocarbon shows were penetrated by the well. However, subsequent well testing recovered no hydrocarbons and the well was plugged and abandoned. Pioneer has earned a 50% participating interest in three permits (Bazma, Jorf and El Hamra) by drilling the Douz #1 well and committing to drill one additional well over the next two years. Pioneer now has the option to operate the three permits.