SK Innovation Co., South Korea's top refiner, said Monday that its wholly owned U.S. subsidiary has bought more than 50 percent stakes in two U.S. oil fields for 387.1 billion won (US$367.7 million). The SK E&P America Inc. acquired a 75 percent stake in an oil field in Grant and Garfield counties, Oklahoma, from U.S. oil developer Plymouth Exploration LLC. The 50 percent stake in an oil field in Crane County, Texas, was bought from another U.S. developer, KA Henry I LLC., it said in an emailed statement