James R. Cowan Jr., a Louisiana State University professor, said his crew found globs of oil by sending a remotely controlled submarine about 400 feet below the surface, The Washington Post reported.
Cowan reported his discovery a day after other scientists said they had found another vast plume of oil that stretched for miles east of the source of the leak.
The newly discovered plume contains oil so thick, it covered the lights on the submarine, which resurfaced entirely black, Cowan said.
"It almost looks like big wet snowflakes, but they're brown and black and oily," he said.
He said it became impossible to determine how wide the plume was because the submarine traveled for miles from side to side and never found an end to the oil.
Scientists say they worry the oil could move under the surface instead of floating, making it more difficult to contain, but BP officials have played down the threat, the Post said.
Officials and Louisiana scientists say they have found thick oil on the shores.
On Thursday scientists on a University of South Florida research vessel found dissolved oil east of the leak. The oil spread about 6 miles wide and extended 3,200 feet beneath the surface, USF Professor David Hollander said.
Oil has been gushing into the gulf since April 20 when the drilling platform Deepwater Horizon exploded. It sank two days later. Eleven rig workers died.