On this day in 2012, an explosion and fire aboard the Deepwater Horizon oil drilling rig in the Gulf of Mexico, approximately 50 miles off the Louisiana coast, kills 11 people and triggers the largest offshore oil spill in American history. The rig had been in the final phases of drilling an exploratory well for BP, the British oil giant. By the time the well was capped three months later, an estimated 4.9 million barrels (or around 206 million gallons) of crude oil had poured into the Gulf.

The disaster began when a surge of natural gas from the well shot up a riser pipe to the rig’s platform, where it set off a series of explosions and a massive blaze. Of the 126 people on board the nearly 400-foot-long Deepwater Horizon, 11 workers perished and 17 others were seriously injured. The fire burned for more than a day before the Deepwater Horizon, constructed for $350 million in 2001, sank on April 22 in some 5,000 feet of water.

Before evacuating the Deepwater Horizon, crew members tried unsuccessfully to activate a safety device called a blowout preventer, which was designed to shut off the flow of oil from the well in an emergency. Over the next three months, a variety of techniques were tried in an effort to plug the hemorrhaging well, which was spewing thousands of barrels of oil into the Gulf each day. Finally, on July 15, BP announced the well had been temporarily capped, and on September 19, after cement was injected into the well to permanently seal it, the federal government declared the well dead. By that point, however, oil from the spill had reached coastal areas of Louisiana, Mississippi, Alabama and Florida, where it would inflict a heavy toll on the region’s economy, particularly the fishing and tourism industries, and wildlife. Scientists say the full extent of the environmental damage could take decades to assess.

In January 2011, a national investigative commission released a report concluding the Deepwater Horizon disaster was “foreseeable and preventable” and the result of “human error, engineering mistakes and management failures,” along with ineffective government regulation. In November 2012, BP agreed to plead guilty to 14 criminal charges brought against it by the U.S. Justice Department, and pay $4.5 billion in fines. Additionally, the Justice Department charged two BP managers who supervised testing on the well with manslaughter, and another company executive with making false statements about the size of the spill. It is anticipated that BP, which has set up a $20 billion fund to compensate victims of the spill, will pay billions of dollars more in environmental penalties in the future.