The largest accidental oil spill in the world began April 20, 2010 when the BP Deepwater Horizon rig exploded in the Gulf of Mexico. Initial estimates reported that only 1,000 barrels of oil per day were being released into the Gulf. These estimates quickly changed to 5,000 barrels per day and then 12,000–19,000 barrels per day by late May. As researchers continued to evaluate the situation, the estimate continued to rise until they determined that an average of 53,000 barrels of oil were released per day between April 20 and July 15, 2010. The final estimate was 5 million barrels of oil flowed into the Gulf of Mexico making it the largest oil spill ever.