An oil sheen about four miles long has appeared in the Gulf of Mexico near the site of the worst oil spill in U.S. history, a Coast Guard spokesman said Thursday. It was not immediately clear where the oil is coming from, said Petty Officer 3rd Class Ryan Tippets. The Coast Guard found out about the oil sheen on September 16 after someone spotted it on a satellite image from the multinational oil and gas company BP, Tippets said. A Coast Guard response team went to the location to collect samples, and sent them to the Coast Guard Marine Safety Lab in Connecticut for testing. Test results are expected in a few weeks, Tippets said.