Chevron Corp., the fourth-largest U.S. oil company, is considering a joint venture with Phillips Petroleum Co.'s chemicals unit and a possible purchase of Phillips' $1.1-billion natural-gas processing division, a person familiar with the situation said. Phillips told investors two weeks ago in New York that it was seeking joint-venture partners for its chemicals unit, which produces resins and basic petrochemicals used in plastics, the person said. A Chevron venture would create a chemicals business with about $5.4 billion in annual sales and link plants on the U.S. Gulf Coast and in Europe and Asia. Spokespersons for San Francisco-based Chevron and Bartlesville, Okla.-based Phillips wouldn't comment. Both companies are looking to cut costs to keep up with larger rivals created by a wave of industry acquisitions.