Royal Dutch Shell says a sheen of oil, 10 square miles in size, has been spotted in the Gulf of Mexico.

Shell (RDSA) said late Wednesday that it reported the sheen to the National Response Center.

Shell said the sheen is one mile wide and ten miles long and is located in the middle of the Gulf of Mexico, between its Mars and Ursa drilling platforms. The platforms are both located 130 miles southeast of New Orleans.