Estimating Gulf of Mexico Oil Spill's Size Proves Slippery Task

(May 14) -- To put it simply, it's a lot.

The specific estimate of how much oil has been leaking into the Gulf of Mexico from a hole caused by an offshore drilling rig's untimely demise has the experts conflicted. The fact of the matter is that there are a lot of numbers out there, and all of them are merely imperfect estimates. With BP trying numerous things to stop the flow of the leak (most recently siphoning the oil), here's a look back at how these estimates evolved.

Preface: Questioning the numbers

"The government has a responsibility to get good numbers. If it's beyond their technical capability, the whole world is ready to help them."

-- Florida State University oceanographer Ian MacDonald, discussing the numbers the government has been using to explain the growth of the oil leak in the Gulf of Mexico. MacDonald and others claim the spill has spewed forth far more than 5,000 barrels a day (still very high), and suggest that the method that the government used to measure the spill was not designed for something this big. For its part, oil company BP suggested that the leak could spew as much as 60,000 barrels a day -- in other words, an Exxon Valdez's worth of oil every four days. -- source

How the story evolved

Date	Estimate
04/21/2010	No leak The initial explosion occurs on the Deepwater Horizon oil rig, leaving 11 missing and presumed dead (the blast was later found to have been caused by a methane bubble). At first the Coast Guard reports that it didn't find an oil leak. Then the rig, which had been on fire since the blast, sinks.
04/22/2010	336,000 gal. The Coast Guard's initial estimate for potential spillage per day after the oil rig sank. BP promises a massive response to the spill, and the search is called off for the 11 missing rig workers.
04/25/2010	42,000 gal. A joint U.S. government and oil industry task force's estimate for potential spillage per day (about 1,000 barrels). In other news, BP tries unsuccessfully to stop the leak using remote-powered submarines, the Coast Guard works on a controlled burn of the oil and NASA takes some satellite photos of the disaster.
04/28/2010	210,000 gal. The National Oceanic and Atmospheric Administration's estimate for spillage per day after reporting the growth of the oil spill is five times worse than originally anticipated (around 5,000 barrels). In response, the White House promises there wouldn't be any new offshore drilling until it finds out why this accident happened.
05/01/2010	1,075,000 gal. Florida State University oceanographer Ian MacDonald's independent estimate of the spillage each day -- five times the amount that NOAA reported (around 25,000 barrels). "I hope I'm wrong. I hope there's less oil out there than that. But that's what I get when I apply the numbers," he says.
05/02/2010	4,200,000 gal. Interior Secretary Ken Salazar's estimate of what the worst-case scenario could be when all is said and done (about 100,000 barrels). However, both he and BP admit they have no clue what the real number might be.
05/04/2010	2,520,000 gal. BP's estimate of the worst-case scenario for spillage per day, a number 12 times bigger than the one given by NOAA less than a week before (about 60,000 barrels). The company discloses this during a congressional hearing where at least one representative, Edward J. Markey, criticizes the inconsistent numbers the company has given.
05/07/2010	13,000,000 gal. MacDonald's estimate for how much oil has spilled in total --- a number that exceeds the 11 million gallons of the Exxon Valdez spill. The BBC suggests, however, that the spill was still relatively small, going by the 5,000-barrel estimate.
05/09/2010	$10 million BP's potential cost per day to clean up the spill, according to company CEO Tony Hayward -- a figure significantly higher than an earlier estimate of $6 million per day. On May 10, the total cost is estimated at $350 million. While the cost is quickly spiraling out of control, it also could be capped if it hits a certain level, thanks to a law passed in the wake of the Exxon Valdez spill.
05/14/2010	2,940,000 gal. An average estimate of the latest total (around 70,000 barrels a day), based on a video BP releases of the oil leak on May 11. Purdue University mechanical engineering professor Steven Wereley analyzed the video for NPR and came up with the total, which has a large margin of error because of the inconsistency of analyzing a video -- it could be as high as 84,000 barrels a day. Another expert tells PBS NewsHour that the level could be as high as 100,000 barrels a day -- or 4.2 million gallons.

Calculating a disaster

Wanna see something scary? Play with this little widget to the left. Put together by PBS NewsHour last week (and last updated Friday), it allows you to take a guess at how much oil has leaked out. Yeah, that's a lot, isn't it?

Ernie Smith is the editor of ShortFormBlog, a news site equally obsessed with numbers and bad jokes.