The biggest oil spill in history was the 1991 Gulf War oil spill, which released an estimated 6 to 8 million barrels (252 to 336 million gallons) of crude oil into the Persian Gulf. Iraqi forces destroyed tankers and oil terminals in Kuwait during the conflict, dwarfing every accidental spill on record by a wide margin. If you’re looking for the largest accidental spill, that title belongs to the 2010 Deepwater Horizon disaster at 3.19 million barrels.
The 1991 Gulf War Spill
During the Gulf War, retreating Iraqi forces opened oil valves and destroyed infrastructure across Kuwait, sending a massive flow of crude into the Persian Gulf. NOAA estimates the total release at 6 to 8 million barrels, with additional oil entering the water as soot and droplets from burning wells onshore. That upper estimate of 336 million gallons is roughly two and a half times the volume of the Deepwater Horizon spill, making this the single largest release of oil into a marine environment ever documented.
Because it was a deliberate act of war rather than an industrial accident, it’s sometimes listed separately from accidental spill rankings. But by sheer volume, nothing else comes close.
Five years after the war, scientists studying the Persian Gulf coast found that intertidal habitats, including salt marshes and mangroves, had suffered extensive damage but were generally recovering. Wading bird populations and seabird breeding success had bounced back in most areas, and petroleum hydrocarbon levels in shallow sediments were declining. The picture wasn’t uniformly positive, though. Sediments at nearly half the sites studied in 1993 still showed high toxicity and elevated petroleum levels, and hydrocarbon concentrations actually increased in parts of the northwestern Gulf between 1992 and 1993 due to resumed tanker traffic.
Deepwater Horizon: The Largest Accidental Spill
On April 20, 2010, an explosion on the Deepwater Horizon drilling rig in the Gulf of Mexico killed 11 workers and triggered an uncontrolled undersea oil gusher. It took 87 days to cap the well, during which 3.19 million barrels (about 134 million gallons) of crude poured into the ocean. This makes it the largest accidental oil spill in history.
The financial fallout was staggering. A federal judge approved a $20.8 billion settlement in 2016, the largest environmental damage settlement in U.S. history. BP also pleaded guilty to 14 felony counts and paid a record $4 billion criminal penalty. On top of the government settlement, BP funded $500 million in research, paid $6.2 billion through its own private claims program to more than 220,000 individuals and businesses, and faced an additional $14.8 billion in private claim payments. The company’s own final estimate of its total costs came to $61.6 billion.
Up to $8.8 billion of the settlement was dedicated specifically to natural resource restoration across the Gulf, funding a science-based plan stretching more than 15 years. That plan included $700 million set aside for damages that weren’t yet known at the time of the agreement.
Other Major Spills for Comparison
The Gulf War and Deepwater Horizon sit well above everything else on the list, but several other spills are historically significant:
- Ixtoc I (1979): An exploratory well blowout in Mexico’s Bay of Campeche released more than 3.4 million barrels of crude into the Gulf of Mexico over nearly 9 months. It was the world’s largest accidental spill until Deepwater Horizon surpassed it three decades later. The spill devastated what had been a nearly pristine marine ecosystem in the Campeche Sound.
- Atlantic Empress (1979): A collision between two supertankers off the coast of Trinidad and Tobago spilled an estimated 287,000 tonnes of oil, making it the largest ship-source spill ever recorded. Because it occurred far offshore, it caused less coastal damage than smaller spills closer to land.
- Hawaiian Patriot (1977): A tanker fire near Hawaii released roughly 31 million gallons (about 738,000 barrels) of crude into the Pacific.
- Exxon Valdez (1989): Perhaps the most famous oil spill in American memory, it was actually much smaller than people assume. The tanker released about 11 million gallons (roughly 262,000 barrels) into Alaska’s Prince William Sound. That’s less than one-tenth the volume of Deepwater Horizon. Its lasting notoriety comes from the pristine, cold-water environment it contaminated and the graphic images of oiled wildlife that dominated news coverage for months.
Why the Exxon Valdez Looms So Large
Many people guess the Exxon Valdez was the biggest spill in history. It wasn’t, not by a long shot. At roughly 40.8 million liters of crude, it doesn’t crack the top five by volume. What made it so devastating was location. Prince William Sound was a cold, remote, nearly pristine ecosystem where oil breaks down extremely slowly. The crude was a medium-weight type with a composition that made it especially persistent in sediments. Decades later, researchers were still finding pockets of weathered oil beneath beaches in the Sound.
The Exxon Valdez also reshaped U.S. oil spill policy. It led directly to the Oil Pollution Act of 1990, which overhauled liability rules and required double-hulled tankers in U.S. waters. In that sense, its impact far exceeded what its volume alone would suggest.
How Regulations Changed After Deepwater Horizon
The Deepwater Horizon disaster exposed serious weaknesses in the blowout preventer, the massive device on the ocean floor designed to seal a well in an emergency. In the aftermath, the U.S. Department of the Interior adopted a series of safety overhauls for offshore drilling.
The 2016 Well Control Rule, later updated, now requires blowout preventers to be capable of sealing the wellbore up to the well’s maximum anticipated pressure at all times. Operators must report equipment failure data to both a government agency and an independent third party, and failure investigations must begin within 90 days. Remotely operated underwater vehicles must be able to open and close each shear ram on a blowout preventer, adding a backup layer of control if surface systems fail. Independent third-party inspectors must submit their qualifications with permit applications, and test results must be delivered to regulators within 72 hours if inspectors can’t witness the tests in person.
These changes don’t eliminate the risk of a catastrophic blowout, but they target the specific mechanical and oversight failures that allowed the Deepwater Horizon well to flow unchecked for nearly three months.