The U.S. Coast Guard said officials have been unable to determine the source of an oil sheen reported in November near the site in the Gulf of Mexico of the 2010 rig explosion and oil spill.
But, it reiterated that an inspection of the well that blew out confirmed again that the tight-fitting cap on the well is secure and no oil is leaking out.
The agency said Tuesday that remotely operated vehicles investigating the sheen concluded operations on Saturday and no sources of leaking oil were identified. During operations, an unidentified substance inconsistent with oil was seen emitting from several areas of the rig wreckage, and samples were collected for further lab analysis, the Coast Guard said.
A prior oil sheen found in September was determined to have come from oil trapped in a containment device that was used in a failed effort to stop the flow of oil to the sea. The device was left on the seafloor and has been there ever since.