Pioneer Natural CEO to retire, be replaced by operating chief Posted by Eric Haun May 19, 2016 U.S. shale oil producer Pioneer Natural Resources Co (PXD) said on Thursday its Chief Executive Officer Scott Sheffield will retire at the end of the year and be replaced by Tim Dove, the company's chief operating officer. Sheffield said he is retiring to spend time with his family. Dove joined a predecessor company to Pioneer in 1994 and has worked there ever since. (Reporting by Ernest Scheyder; Editing by Marguerita Choy) Email