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BP Oil Spill Left Rhode Island-Sized 'Bathtub Ring' on Seafloor: Study

New research shows that the BP oil spill left an oily "bathtub ring" on the sea floor that's about the size of Rhode Island. The study by UC Santa Barbara’s David Valentine, the chief scientist on the federal damage assessment research ships, estimates that about 10 million gallons of oil coagulated on the floor of the Gulf of Mexico around the damaged Deepwater Horizons oil rig. Valentine said the spill left other splotches containing even more oil. The rig blew on April 20, 2010, and spewed 172 million gallons of oil into the Gulf through the summer. Scientists are still trying to figure where all the oil went and what effects it had. The study appears in Monday's Proceedings of the National Academy of Sciences.

BP disputed the researcher's findings. "The authors failed to identify the source of the oil, leading them to grossly overstate the amount of residual Macondo oil on the sea floor and the geographic area in which it is found," the company said in a statement to NBC News. "Instead of using rigorous chemical fingerprinting to identify the oil, the authors used a single compound that is also found in every natural oil seep in the Gulf of Mexico, causing them to find false positives all over the sea floor." BP also said the researchers' mapping technique "dramatically overestimates" the impacted area.

Four years later, BP oil spill still wreaking havoc 2:25

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— The Associated Press and NBC News staff