The following is a timeline of the Deepwater Horizon oil spill (also referred to as the BP oil spill, the Gulf of Mexico oil spill or the Macondo blowout). It was a massive oil spill in the Gulf of Mexico, the largest offshore spill in U.S. history. It was a result of the well blowout that began with the Deepwater Horizon drilling rig explosion on April 20, 2010.