A study released this month about the distribution of oil and gas from the 2010 Deepwater Horizon spill in the Gulf of Mexico has found that the largest percentage of the spill—36 percent—never rose out of the underwater plume estimated at 3,300 to 4,300 feet below the surface; and that the slick visible on the surface only represented about 15 percent of the total leaked gas and oil.
The Sarasota Herald-Tribune quoted the lead author of the study, which was published in Proceedings of the National Academy of Sciences:
"The visible surface slick that people were riveted by during the months of the spill was really only 15 percent of the total mass," said Thomas Ryerson, a research chemist with the National Oceanic and Atmospheric Administration.
The study found the airborne plume made up another seven percent, but about a quarter of the total spill remains unaccounted for.
The Tribune added, "The study also provides critical benchmarks, such as the ratio of oil to gas, that will prove important as the federal government seeks money from BP to pay for the response and recovery."
A ScienceDaily summary of the study explains more:
When combined, the data tell a story about the fate of the oil and gas in the air, on the surface and in the ocean and enabled a new chemistry-based spill rate estimate of an average of 11,130 tons of gas and oil compounds per day -- close to the official average leak rate estimate of about 11,350 tons of gas and oil per day (equal to about 59,200 barrels of liquid oil per day). In total, approximately 4.2 million barrels of oil were released from the well.