Last April's oil spill in the Gulf of Mexico was ultimately the world's largest, spilling 205 million gallons of oil from April through July, 2010. The Gulf of Mexico oil spill beat the previous record holder by more than 60 million gallons of oil. The world's second largest spill was the Ixtoc I Oil Well in 1979 which also took place in the Gulf of Mexico. Take a look at this list of the 15 largest oil spills.

Comments
Like the sources you cite, you are mixing “oil spills,” where oil is spilled in transit, and blowouts/gushers, where oil is released under its own natural pressure. In fact some of your sources seem to think that only a ship can create an “oil spill.” The Lakeview gusher of 1910-11 is still the greatest blowout, exceeding last year’s BP blowout by several times. And neither was an “oil spill” except in the loosest sense.