How do you count the barrels of spilled BP oil in the Gulf?

Answers to your questions about the news.
June 21 2010 5:24 PM

100 Million Barrels of Oil in the Well, 100 Million Barrels of Oil

If one of those barrels should happen to spill ...

Read Slate's  complete coverage of the BP oil spill.

Oil spill. Click image to expand.
Booms collect oil from the Gulf spill

Shortly after the Deepwater Horizon rig exploded on April 20, the federal government estimated that the Macondo well was spilling approximately 5,000 barrels of oil a day into the Gulf of Mexico, based on aerial photographs. (One barrel contains 42 gallons.) Since then, the estimates have floated steadily upward. BP now says that the worst-case scenario would be 100,000 barrels a day, if the blowout preventer were removed. These numbers raise several questions, not least of which is ...

Why is it important to know precisely how much oil has spilled?
Because BP will be paying fines by the barrel. The company faces several sources of liability: cleanup costs, irremediable damage to property and the environment, and civil and criminal penalties on both the federal and state levels. The federal civil fines are pegged to the precise amount of oil spilled. The Clean Water Act charges polluters up to $1,100 per barrel, or $4,300 if gross negligence caused the accident. (The statute doesn't define "gross negligence," although it does define oil, barrel, and United States.)


The exact volume of the spill impacts the other liability categories only indirectly. The first step (PDF) in any cleanup operation is to evaluate the size of the spill, usually in gallons. That number dictates how many people and what sort of equipment will be required. The government has also established a formula (PDF) to monetize the environmental damage from a spill, but that is designed for "small discharges"—up to 50,000 gallons, or 1,200 barrels. (BP has been spilling at least 10 times that much oil every single day.

When BP recovers oil from the water, does that get subtracted from the total spill numbers?
Sort of. The law doesn't mention oil that is sucked out of the ocean, so in principle the civil fines are based on whatever gets spilled, regardless of the cleanup. That said, judges can—and often do—reduce the size of a penalty based on what's been recovered, the level of fault involved, and damages the defendant has to pay under other provisions. So BP will likely get some credit for the recovered oil and won't have to pay $258 million per day in civil fines.

Who gets the final say on how much oil was spilled?
A federal judge, probably. When the EPA files its suit against BP, it will include an estimate of the total oil spilled as part of its penalty calculation. The government's asking price is sure to be astronomical, in light of public sentiment, so an out-of-court settlement seems unlikely. If the case goes to trial, BP's experts will argue with government scientists over the number of barrels of oil that were released into the Gulf. The judge will have to pick a side or come up with her own number.

The litigants may opt for a jury, but that's not likely. A judge is better prepared to handle these technical issues, and juries can really slow a trial down. BP might also fear the wrath of 12 angry Louisianans. But juries can be unpredictable. An Anchorage jury acquitted the captain of the Exxon Valdez of most of the charges against him.

How will the EPA estimate the total volume of the spill?
No one knows yet. There is no gold standard for measuring oil flow at this depth. The Macondo spill involves far more oil, and much deeper, than any other that ended up being litigated under the Clean Water Act. Ninety-nine percent of oil spills in the United States involve less than 240 total barrels of oil. The only comparable disaster is the 1979 Ixtoc oil spill near Mexico. The current civil fine system wasn't in effect at that time, and, even if it had been, the law applies only inside the U.S. exclusive economic zone, which extends 200 nautical miles from our shores.

Unless a new technique comes along before trial—the statute of limitations is five years, but the legal process might extend beyond that—the judge will have to endorse one of the current methodologies or settle on a compromise estimate.

Scientists are currently employing five different approaches. A team led by Energy Secretary Steven Chu is analyzing pressure readings inside the blowout preventer. Another group is looking at video of the leak to determine the velocity of the particles escaping the well. A third team continues to analyze infrared images of the oil that has made its way to the surface, correcting for the amount that has been burned off, dispersed, skimmed, or evaporated. Still others have used geological data about the well and the conditions surrounding to build a computer model that compares Macondo to similar wells that have leaked on a smaller scale in the past. Finally, a team at the Woods Hole Oceanographic Institution is using sonar-equipped robots to measure the plumes surging from the well. The current estimates range from 12,600 barrels a day to 125,000 barrels a day, although natural gas, sediments, and water from inside the well constitute about one-half of the higher estimate.

Got a question about today's news? Ask the Explainer.

Explainer thanks Tracy Hester of the University of Houston Law Center.

Like  Slate and the Explainer on Facebook. Follow us on Twitter.

Brian Palmer writes about science, medicine, and the environment for Slate and the Natural Resources Defense Council. Email him at Follow him on Twitter.



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