Common use of Xxxx Clause in Contracts

Xxxx. Xx. Xxxx xxxame Executive Vice President -- Business Development of Pioneer and Pioneer USA in August 1997. He was also appointed a director of Pioneer USA in August 1997. Mr. Xxxx xxxned Parkxx & Xarsxxx xx May 1994 as Vice President -- International and was promoted to Senior Vice President -- Business Development in October 1996, in which position he served until August 1997. Prior to joining Parkxx & Xarsley, Mr. Xxxx xxx employed with Diamond Shamrock Corp., and its successor, Maxus Energy Corp, in various capacities in international exploration and production, marketing, refining and marketing and planning and development. Mr. Xxxx xxxned a B.S. in Mechanical Engineering from Massachusetts Institute of Technology in 1979 and received his M.B.A. in 1981 from the University of Chicago. 21 157

Xxxx. Xx. Xxxx xxxame Executive Vice President -- Business Development of Pioneer and Pioneer USA in August 1997. He was also appointed a director of Pioneer USA in August 1997. Mr. Xxxx xxxned Parkxx & Xarsxxx xx May 1994 as Vice President -- International and was promoted to Senior Vice President -- Business Development in October 1996, in which position he served until August 1997. Prior to joining Parkxx & Xarsley, Mr. Xxxx xxx employed with Diamond Shamrock Corp., and its successor, Maxus Energy Corp, in various capacities in international exploration and production, marketing, refining and marketing and planning and development. Mr. Xxxx xxxned a B.S. in Mechanical Engineering from Massachusetts Institute of Technology in 1979 and received his M.B.A. in 1981 from the University of Chicago. 21 157.

Xxxx. Xx. Xxxx xxxame Executive Vice President -- Business Development of Pioneer and Pioneer USA in August 1997. He was also appointed a director of Pioneer USA in August 1997. Mr. Xxxx xxxned Parkxx & Xarsxxx xx May 1994 as Vice President -- International and was promoted to Senior Vice President -- Business Development in October 1996, in which position he served until August 1997. Prior to joining Parkxx & Xarsley, Mr. Xxxx xxx employed with Diamond Shamrock Corp., and its successor, Maxus Energy Corp, in various capacities in international exploration and production, marketing, refining and marketing and planning and development. Mr. Xxxx xxxned a B.S. in Mechanical Engineering from Massachusetts Institute of Technology in 1979 and received his M.B.A. in 1981 from the University of Chicago. 21 15720 156

Xxxx. Xx. Xxxx xxxame Executive Vice President -- Business Development of Pioneer and Pioneer USA in August 1997. He was also appointed a director of Pioneer USA in August 1997. Mr. Xxxx xxxned Parkxx & Xarsxxx xx May 1994 as Vice President -- International and was promoted to Senior Vice President -- Business Development in October 1996, in which position he served until August 1997. Prior to joining Parkxx & Xarsley, Mr. Xxxx xxx employed with Diamond Shamrock Corp., and its successor, Maxus Energy Corp, in various capacities in international exploration and production, marketing, refining and marketing and planning and development. Mr. Xxxx xxxned a B.S. in Mechanical 20 156 Engineering from Massachusetts Institute of Technology in 1979 and received his M.B.A. in 1981 from the University of Chicago. 21 157.

Xxxx. Xx. Xxxx xxxame Executive Vice President -- Business Development of Pioneer and Pioneer USA in August 1997. He was also appointed a director of Pioneer USA in August 1997. Mr. Xxxx xxxned Parkxx & Xarsxxx xx May 1994 as Vice President -- International and was promoted to Senior Vice President -- Business Development in October 1996, in which position he served until August 1997. Prior to joining Parkxx & Xarsley, Mr. Xxxx xxx employed with Diamond Shamrock Corp., and its successor, Maxus Energy Corp, in various capacities in international exploration and production, marketing, refining and marketing and planning and development. Mr. Xxxx xxxned a B.S. in Mechanical 21 157 Engineering from Massachusetts Institute of Technology in 1979 and received his M.B.A. in 1981 from the University of Chicago. 21 157.

Xxxx. Xx. Xxxx xxxame Executive Vice President -- Business Development of Pioneer and Pioneer USA in August 1997. He was also appointed a director of Pioneer USA in August 1997. Mr. Xxxx xxxned Parkxx & Xarsxxx xx May 1994 as Vice President -- International and was promoted to Senior Vice President -- Business Development in October 1996, in which position he served until August 1997. Prior to joining Parkxx & Xarsley, Mr. Xxxx xxx employed with Diamond Shamrock Corp., and its successor, Maxus Energy Corpcorp., in various capacities in international exploration and production, marketing, refining and marketing and planning and development. Mr. Xxxx xxxned a B.S. in Mechanical Engineering from Massachusetts Institute of Technology in 1979 and received his M.B.A. in 1981 from the University of Chicago. 21 157

Xxxx. Xx. Xxxx xxxame Executive Vice President -- Business Development of Pioneer and Pioneer USA in August 1997. He was also appointed a director of Pioneer USA in August 1997. Mr. Xxxx xxxned Parkxx & Xarsxxx xx May 1994 as Vice President -- International and was promoted to Senior Vice President -- Business Development in October 1996, in which position he served until August 1997. Prior to joining Parkxx & Xarsley, Mr. Xxxx xxx employed with Diamond Shamrock Corp., and its successor, Maxus Energy Corp, in various capacities in international exploration and production, 21 157 marketing, refining and marketing and planning and development. Mr. Xxxx xxxned a B.S. in Mechanical Engineering from Massachusetts Institute of Technology in 1979 and received his M.B.A. in 1981 from the University of Chicago. 21 157.

Xxxx. Xx. Xxxx xxxame Executive Vice President -- Business Development of Pioneer and Pioneer USA in August 1997. He was also appointed a director of Pioneer USA in August 1997. Mr. Xxxx xxxned Parkxx & Xarsxxx xx May 1994 as Vice President -- International and was promoted to Senior Vice President -- Business Development in October 1996, in which position he served until August 1997. Prior to joining Parkxx & Xarsley, Mr. Xxxx xxx employed with Diamond Shamrock Corp., and its successor, Maxus Energy Corp, Corp. in various capacities in international exploration and production, marketing, refining and marketing and planning and development. Mr. Xxxx xxxned a B.S. in Mechanical 21 157 Engineering from Massachusetts Institute of Technology in 1979 and received his M.B.A. in 1981 from the University of Chicago. 21 157.