US officials have confirmed what many have widely feared: the BP oil spill in the Gulf of Mexico is the worst oil spill in US history. On Thursday, the US Geological Survey said the well has been spewing between 504,000 and more than a million gallons of oil a day. That means a minimum 19 million gallons have spilled into the Gulf over the past five weeks, easily surpassing the size of the 1989 Exxon Valdez disaster in Alaska. The highest estimate would mean a spill of nearly 39 million gallons.