Two hundred ten million gallons is a lot of oil. So much so that four years after the Deepwater Horizon spill, it can still be seen on the ocean floor of the Gulf of Mexico.
That's according to a new study, which says the 2010 spill - the biggest oil spill in history - left what it calls a "bathtub ring" on the gulf.
The study says hydrocarbons from the oil plume of the well have contaminated an area of some 1,200 square miles in the deep waters of the gulf.
The study's lead author David Valentine spoke on how the geography of the ocean floor in the gulf, keeps the residual oil in the gulf.
Deepwater Horizon Bathtub Ring
Deepwater Horizon's footprint actually a 'bathtub ring'
FILE - In this Wednesday, April 21, 2010 file photo, oil can be seen in the Gulf of Mexico, more than 50 miles southeast of Venice on Louisiana's tip, as a large plume of smoke rises from fires on BP's Deepwater Horizon offshore oil rig. An April 20, 2010 explosion at the offshore platform killed 11 men, and the subsequent leak released an estimated 172 million gallons of petroleum into the gulf. U.S. District Judge Carl Barbier ruled Thursday, Sept. 4, 2014, in New Orleans, La., that BP acted recklessly and bears most of the responsibility for the oil spill. The ruling exposes BP to about $18 million in civil fines under the Clean Water Act. (AP Photo/Gerald Herbert, File)
PJ Hahn, Coastal Zone Manager for Plaquemines Parish, examines oil along the shoreline of Bay Jimmy, which was heavily impacted by the Deepwater Horizon oil spill, in Plaquemines Parish, La., Friday, Sept. 27, 2013. The methods that BP employed during its 86-day struggle to stop oil gushing into the Gulf of Mexico will be the focus of a trial resuming Monday, Sept. 30, 2013 in New Orleans, in the high-stakes litigation spawned by the worst offshore spill in the United States. (AP Photo/Gerald Herbert)
In this Monday, June 7, 2010 photo, patches of oil from the Deepwater Horizon spill are seen from an underwater vantage, Monday, June 7, 2010, in the Gulf of Mexico south of Venice, La.. (AP Photo/Rich Matthews)
In this Monday, June 7, 2010 photo, patches of oil from the Deepwater Horizon spill are seen from an underwater vantage, in the Gulf of Mexico south of Venice, La.. (AP Photo/Rich Matthews)
Patches of oil from the Deepwater Horizon spill are seen from an underwater vantage, Monday, June 7, 2010, in the Gulf of Mexico south of Venice, La.. (AP Photo/Rich Matthews)
FILE - In this Monday, June 7, 2010 file photo, patches of oil from the Deepwater Horizon spill are seen from an underwater vantage, in the Gulf of Mexico, south of Venice, La. In a federal court hearing Wednesday, Sept. 24, 2014, in New Orleans, U.S. District Judge Carl Barbier ruled BP PLC must stick by an agreement with companies that got payouts after claiming the 2010 Gulf oil spill hurt their business. His ruling thwarts BP's latest attempt to control its soaring liability from the spill, which may be nearing $50 billion. (AP Photo/Rich Matthews, File)
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"At this depth of 3,000 or 4,000 feet, it's bounded on three sides so there's no current that flushes through ... Water tends to slosh back and forth," Valentine said.
So if the water sloshes around the gulf, like in a bathtub, and takes the oil with it, it makes sense that there'd be a bathtub ring around the gulf. And it's easy to see in samples from the ocean floor.
BP has unsurprisingly disputed the study's findings, saying the researchers haven't been able to distinguish between oil from the spill and naturally occurring oil in the gulf.
But Valentine told The Times-Picayune the oil from the well was easy to trace because, "The discharge from the Macondo well simply swamped the signal from other sources in a clear and distinctive way that points right to the Macondo well as source."
BP has plenty of incentive to try to downplay the study's findings. It's still wrestling with the legal fallout of the spill as the affected gulf states try to get compensation for the damage.