Complex sentence: Cenovus co-owns two refineries in the United States with Phillips 66 at 50%: the Wood River Refinery (Illinois) and Borger, Texas refinery which Phillips 66 operates.
Split into simpler sentences: Cenovus co-owns two refineries in the United States with Phillips 66. Cenovus has a 50 percent interest in the Wood River Refinery (Illinois) and Borger, Texas refineries which Phillips 66 operates.