The Deepwater Horizon blowout killed 11 and became the largest marine oil spill ever

On April 20, 2010, the Deepwater Horizon, an offshore drilling rig operated by Transocean under contract to BP, was finishing work on the Macondo well in the Gulf of Mexico. A surge of natural gas burst through the well's barriers, ignited, and exploded, killing 11 workers and injuring others. The rig sank two days later, and the well, uncapped on the seafloor, began gushing oil.

The blowout was the result of a series of failures and decisions that compromised the well's safety barriers. Investigations found that the cement job sealing the well (by Halliburton) was faulty, that critical negative-pressure tests had been misread, and that cost-cutting and time pressure had influenced decisions about the well's design and the number of centralizers used. Multiple barriers that should have prevented a blowout failed in sequence.

The oil spilled for 87 days before the well was finally capped — nearly 5 million barrels (about 210 million gallons), the largest marine oil spill in history. The environmental and economic damage to the Gulf Coast was enormous. BP's total costs reached about $65 billion, including cleanup, fines and compensation. The disaster became a defining case of how cost-cutting, misread data and failed safety barriers can combine into a catastrophe.