Why the BP Spill is Bigger Than You Think

Oil companies measure spills in barrels. In gallons, it adds up to a lot more.

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Americans are notoriously bad at math, so it may come as a shock to learn that the BP oil spill in the Gulf of Mexico is 42 times bigger than many people might have believed.

It's not just because of the ballooning guesstimates of the size of the spill. It's also because the standard unit of measurement for oil makes the volume of goo sound smaller than it is, at least to the untutored ears of anybody who doesn't pump or process oil for a living.

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The oil industry measures crude in barrels, and the government has adopted the industry standard for purposes of describing the spill. Right after the disaster occurred on April 20, we heard that about 1,000 barrels a day were spilling into the Gulf. That didn't sound catastrophic, but of course the figure has rocketed upward, thanks to information revealed by the BP spillcam we've all found oddly mesmerizing. The latest estimate is 60,000 barrels a day. Big increase. Big number. About the same as the number of minutes in six weeks. Or about 15 times the number of Tweets sent out by Kim Kardashian in her Twitter career.

But who conceptualizes liquid in terms of barrels? Most Americans don't. We think of gallons. Of gas, milk, bleach, antifreeze, even wine. And it turns out there are 42 gallons in one barrel of oil. That's a big multiplier. To help with visualization, I checked the specs on the American Standard Lifetime bathtub, available at Home Depot for $699. It's about average size, with a capacity of 59 gallons. So if 60,000 barrels is the right number, that means about 2,520,000 gallons is pouring out of the well every day. At that rate, the flow of oil would completely fill a Lifetime bathtub every two seconds.

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If 60,000 barrels spilled out of the well every day, that would amount to 3,600,000 barrels by now. But a lot more gallons. At the 60-day point (June 19), the spill would add up to 151,000,000 gallons. At 90 days (July 19), it would be 227,000,000 gallons. How much is that? This gets silly, but if it were gasoline, 151,000,000 gallons would be enough to fuel 315,000 typical sedans getting 25 miles per gallon for an entire year. It would fill about 2,600,000 Lifetime bathtubs, or 5,800 Heritage Oval Platinum pools ($3,499), the biggest sold by Wal-Mart. Interestingly, 151,000,000 gallons of oil would only fill the New Orleans Superdome about one-sixth of the way. Still, you wouldn't want to be sitting in the high seats, even if they were dry.

The media mixes barrels and gallons, which makes it confusing to keep track of how much oil we're talking about. To make it more fun, some industry people measure oil in metric tonnes, which is weight, not volume. As near as I can tell, one metric tonne of oil equals about seven barrels, or 294 gallons. But my mental blowout preventer fails when I try to convert weight to volume and metric to American all at once. So I stick to gallons, and I've gotten into the habit of mentally multiplying by 42 every time I see the quantity expressed in barrels. To make the math easier, multiply by 50 and subtract a little. It's not like precision matters. It's just oil.

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Here's how BP's Gulf spill compares with a few similar disasters, based on what we know so far. All of these numbers are approximate, since oil workers don't usually attach a measuring device to a well right before a spill:

Incident Barrels Gallons Lifetime bathtubs
BP spill, Gulf of Mexico, 2010 (as of Day 60, guesstimate) 3,600,000 151,000,000 2,600,000
Exxon Valdez, 1989 257,000 10,800,000 182,949
Ixtoc 1, Gulf of Mexico, 1979 3,000,000 126,000,000 2,135,593
Santa Barbara spill, 1969 80,000 3,360,000 56,949

As BP CEO Tony Hayward has pointed out, the Gulf of Mexico is "a very big ocean." It contains something like 643 quadrillion gallons of sea water, a number that I think looks like this: 643,000,000,000,000,000. That's huge compared with the mere 151,000,000 gallons of oil or so that has spilled into it. Then again, try putting a single drop of oil in a glass of water and drinking it. Suddenly a little seems like a lot.