reporters Thursday . One team looked at the oil on the surface and came up with the estimate of 12,000 to 19,000 barrels per day . A second team used a different method and came up with a range of 12,000 to 25,000 barrels per day , McNutt said . The official estimate uses the range where the estimates overlap . The lower end of the government estimate -- 12,000 barrels per day -- would mean that about 18.6 million gallons of oil has been spilled since the April 20 oil rig explosion that started the leak . The higher end -- 19,000 barrels per day -- would mean 29.5 million gallons has been spilled . The Exxon Valdez spilled about 11 million gallons of oil . Worldwide , there have been more than a dozen bigger oil spills than the Gulf spill . The worst was the destruction of Kuwaiti terminals and tankers by Saddam Hussein 's forces during the 1991 Gulf war , which spilled 240 million gallons , according to the Oil Spill Intelligence Report . The amount of oil spilled could have very specific financial ramifications for BP . If the government finds the company negligent
-LRB- CNN -RRB- -- The Gulf of Mexico undersea gusher is the largest oil spill in United States history -- possibly already more than twice as big as the Exxon Valdez spill , government estimates suggested Thursday . 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 told reporters Thursday . 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 . It 's also the more conservative estimate of two reached by two separate teams of government scientists who used two different methods , McNutt told