Scientists observed 130,000 to 270,000 barrels of oil on the water's surface on May 17, and think a similar amount had already been burned, skimmed, dispersed or evaporated.

That would mean 260,000 to 540,000 barrels had leaked as of 10 days ago. The Exxon Valdez leaked about 250,000 barrels into Alaska's Prince William Sound in 1989.

The busted well is spewing oil at a rate of at least 12,000 to 19,000 barrels a day, U.S. Geological Survey Chief Marcia McNutt said on May 27.

A barrel of oil has 42 gallons, so that's 504,000 to 798,000 gallons a day.

That's more than twice as much as previous estimates, which put the rate at 5,000 barrels, or 210,000 gallons, per day.