Grist: More than three years after the Deepwater Horizon exploded, triggering the worst oil spill in American history, the sunken wreckage of the rig may still be leaking oil into the Gulf of Mexico.
Beginning in the fall of last year and continuing through the winter, mysterious oil sheens were spotted in the vicinity of the rig wreckage.
A team of researchers set about trying to figure out exactly where the oil was coming from by studying its chemical composition. They matched the slicks to samples...