Over 5 million barrels of oil was released into the ocean during the BP Deepwater Horizon oil spill, and up to 620,000 barrels may now be on the ocean floor, a new study finds.

The study, done by geochemists at the University of California, Santa Barbara, looked at sediment samples from the Gulf of Mexico and located evidence of the chemical Hopane, which indicates the presence of crude oil. It was known that 2 million barrels of the 5 million barrels spilled had not been collected, and the researchers determined between 4 and 31 percent of the 2 million barrels has reached the ocean floor.

“When oil first began to shoot out of the broken well, some 2 million barrels’ worth broke up into microscopic droplets before reaching the surface and became suspended in the deep ocean,” Mother Jones reports. The study shows at least some of this oil that was stuck at a certain depth has reached the bottom of the Gulf of Mexico.

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