However, no sources of leaking oil were identified during BP's recent weeklong mission to inspect the undersea wells and wreckage from the 2010 explosion and oil spill, the Coast Guard said.
The exact composition of the leaking substance and the rate of leakage is not yet known, CBS News reported Wednesday.
Because it is not thought to be oil it cannot be the source of recurring oil sheens recently observed in the area of the Deepwater Horizon, the Coast Guard, which oversaw BP's inspection, said.
"No apparent source of the surface sheen has been discovered by this effort," Capt. Duke Walker said of the inspection mission.
BP has collected samples of the leaking substance with remotely operated vehicles for further laboratory analysis while the oil sheen on the ocean's surface is being monitored by satellite, the Coast Guard said.
"Next steps are being considered as we await the lab results of the surface and subsurface samples and more detailed analysis of the video shot during the mission," Walker said.