Chevron Products Co., a division of Chevron U.S.A. Inc., announced Tracey Gardiner succeeded Cary Knuth as vice president of base oils on Jan. 1. The company also named Luyen Vo marketing and business development manager, immediately succeeding Brent Lok, who will retire this April. Bradford, Pennsylvania-basedAmerican Refining Group Inc.said Jon Giberson will succeed Jeannine Schoenecker as president and chief operating officer.Chevron Phillips Chemical Co.announced Carolyn Burke as senior vice president and chief financial officer effective Feb. 13.