When It Comes to Spills, Size Counts, but Is Often Elusive


Even after BP PLC’s broken well under the Gulf of Mexico stops spewing, we might never know how much oil spilled.

The extent of earlier spills of comparable magnitude remains disputed, even though they were easier to analyze. Oil companies don’t have much incentive to measure spills accurately, and government officials haven’t always needed to get a reliable count.

Exxon knew how much oil its Valdez tanker held when it ran aground 21 years ago. And yet some Alaskan scientists and environmental advocates who have studied the spill say the true amount spreading through Prince William Sound was two or three times the commonly accepted total.

Determining the size of the BP spill will be crucial because under a federal law passed in the wake of the Valdez disaster, oil companies pay penalties that are directly proportional to the amount of oil released into the water.

Yet the size of the current disaster is far more difficult to calculate than previous spills, because no one knows for sure how much crude was contained in the reservoir thousands of feet below the water’s surface, nor whether the oil has been spewing at a constant rate.

“Based on the history of past large spills, I am sure there will be differences of opinion on the exact amount that was spilled,” says William J. Lehr, senior scientist in the National Oceanic and Atmospheric Administration’s Office of Response and Restoration, and a member of the federal group estimating the amount of oil spilled in the Gulf. “We give the best scientific estimate we can, under tight time constraints and with the data available at the time.”

To put the Gulf oil spill in perspective, it often is compared with the Exxon Valdez disaster. But the scope of the 1989 event is still up in the air.

Soon after the spill, Exxon put the total volume of oil released into the water at 10.8 million gallons, or 250,000 barrels.

The company came up with that figure by subtracting the volume of remaining liquid offloaded from the tanker after the accident from the total size of the initial cargo. The problem with this approach, say some scientists and Alaska environmental advocates, is that the removed liquid contained a lot of seawater that had entered the tanker through the punctured hull, potentially inflating the leftover liquid in the ship and diminishing the estimated spill size.

Craig Tillery, deputy attorney general for the civil division of Alaska’s Department of Law, confirms that the 10.8 million figure didn’t take into account water. How much, he says the state never bothered to confirm.

“The state was in the process of getting that information when we settled the case,” Mr. Tillery says. “We didn’t ever get it—we had no need for it, at least in terms of litigation.”

An Exxon Mobil spokeswoman says only that 10.8 million gallons “is the number that was agreed upon at the time.” She declined to comment on claims that it is an underestimate.

Other massive spill totals also come with big question marks attached. A half century of small spills in the Niger Delta added as much as to 1.5 million tons of oil (nine million to 13 million barrels), according to a 2006 report by scientists from Nigeria, the U.K. and the U.S. But that widely reported total was based on extrapolations from incomplete Nigerian government records covering only a third of the relevant years.

“It is very difficult to get accurate figures,” says Clive Wicks, a consultant for the environmental group WWF UK and a study co-author. Indeed, a follow-up study conducted two years later found that the total amount over 50 years could have been as little half the size previously thought.

A major spill, in Brooklyn, N.Y., in the late 1970s is frequently put at 17 million gallons, or about 420,000 barrels, but an Environmental Protection Agency report in 2007 cautioned that the estimate, produced by the Coast Guard in 1979, appears to be too low. The true amount might be as much as 30 million gallons, the EPA said, based on amounts of oil recovered since then.

Despite scientists’ efforts, the true size of the BP spill likely will remain elusive. Early estimates were based on low-quality video and rough approximations from plume sizes. And in the early days of the spill, there were no reliable numbers at all.

One problem with coming up with a definitive number is that assessments of how much oil is flowing from the runaway well are in flux. The scientists assigned by the federal government to measure the rate of flow put that number at 35,000 to 60,000 barrels per day in their latest estimate last week. That is a big increase from a projection of 12,000 to 19,000 barrels a day a few weeks earlier.

The Numbers Guy Blog

NOAA’s Dr. Lehr said these estimates are intended solely to aid recovery efforts. A separate federal team will assess the damage for purposes of fines and litigation.

The spillage total is critical because BP can be charged $1,100 to $4,300 a barrel spilled, under the Clean Water Act.

The amount spilled also informs the Natural Resource Damage Assessment, which will be used to determine how much BP will have to pay for environmental damage. A BP spokesman referred questions about potential fines to the government, saying the company is focused on recovery efforts.

Several government agencies didn’t respond to requests for comment.

“We’re focused really hard on cleaning up, and making things right,” says BP spokesman John Curry.

Correction & Amplification:

The Clean Water Act provides for fines of $1,100 to $4,300 per barrel of oil spilled. An earlier version of this column said that BP could be fined under the act at a rate of $1,100 to $4,300 per gallon of oil spilled.

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Stuart H. Smith is an attorney based in New Orleans fighting major oil companies and other polluters.
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