The U.S. Coast Guard this week said it issued a notice to Transocean of the possible release of oil from debris of the sunken Deepwater Horizon oil rig.
The rig caught fire and sank last year in the Gulf of Mexico, killing 11 workers and leading to one of the worst environmental disasters in the history of the industry.
The Coast Guard said it didn't find evidence the release came from the underwater well, though Transocean claimed there was "no question" it came from BP's Macondo well.
"As owner and operator, BP is the responsible party for all fluids that emanated from the Macondo well head and BP has repeatedly acknowledged that responsibility," the company was quoted by London's Daily Telegraph as stating.
BP said the Macondo well wasn't the source of oil sightings in the Gulf of Mexico.
A government report on the April 2010 disaster found BP, Transocean and Halliburton violated safety regulations prior to the spill. It determined that the blowout that led to the gas explosion that sunk the platform came from the failure of a cement barrier associated with the well.
Transocean in June said BP didn't verify that Halliburton tested the cementing process.