When the Deepwater Horizon oil rig sank in the Gulf of Mexico on April 22, 2010, no one was prepared for the massive environmental disaster that followed. We can see how the Gulf oil spill, the worst environmental disaster in U.S. history, stacks up against the world's worst oil spills.

13. The Torrey Canyon Oil Spill

When: March 18, 1967

Where: Scilly Isles, U.K.

Amount spilled: 25-36 million gallons

The Torrey Canyon was one of the first big supertankers, and it was also the source of one of the first major oil spills. Although the ship was originally built to carry 60,000 tons, it was enlarged to a 120,000-ton capacity, and that’s the amount the ship was carrying when it hit a reef off the coast of Cornwall.

The spill created an oil slick measuring 270 square miles, contaminating 180 miles of coastland. More than 15,000 sea birds and enormous numbers of aquatic animals were killed before the spill was finally contained.

Toxic solvent-based cleaning agents were used by Royal Navy vessels to try to disperse the oil, but that didn't work very well and instead caused a great deal of environmental damage. It was then decided to set fire to the ocean and burn away the oil by dropping bombs.

12. The Sea Star Oil Spill

When: Dec. 19, 1972

Where: Gulf of OmanAmount spilled: 35.3 million gallons

The South Korean supertanker, Sea Star, collided with a Brazilian tanker, the Horta Barbosa, off the coast of Oman on the morning of Dec. 19, 1972. The vessels caught fire after the collision and the crew abandoned ship. Although the Horta Barbosa was extinguished in a day, the Sea Star sank into the Gulf on Dec. 24 following several explosions.

11. Odyssey Oil Spill

When: Nov. 10, 1988

Where: Off the coast of Nova Scotia, CanadaAmount spilled: 40.7 million gallons

This large oil spill occurred about 700 nautical miles off the coast of Newfoundland and spilled more than 40 million gallons of oil into the ocean.

10. M/T Haven Tanker Oil Spill

When: April 11, 1991

Where: Genoa, ItalyAmount spilled: 45 million gallons

This oil tanker exploded and sank off the coast of Italy, killing six people and leaking its remaining oil into the Mediterranean for 12 years. The source of the explosion was thought to be the ship’s poor state of repair — supposedly the Haven was scrapped after being hit by a missile during the Iran-Iraq War, but was put back into operation.

9. ABT Summer Oil Spill

When: May 28, 1991 Where: About 700 nautical miles off the coast of AngolaAmount spilled: 51-81 million gallons

This ship exploded off the coast of Angola, discharging massive amounts of oil into the ocean. Five of the 32 crew members on board died as a result of the incident. A large slick covering an area of 80 square miles spread around the tanker and burned for three days before the ship sank on June 1, 1991. Subsequent efforts to locate the wreckage were unsuccessful.

8. Amoco Cadiz Oil Spill

This oiled beach in Brittany is the result of the Amoco Cadiz oil spill. Wikimedia Commons

When: March 16, 1978

Where: Portsall, France

Amount spilled: 69 million gallons

The massive Amoco Cadiz was caught in a winter storm that damaged the ship’s rudder. The ship put out a distress call, but while several ships responded, none were able to prevent the ship from running aground. On March 17, the gigantic supertanker broke in half, sending its 69 million gallons of oil into the English Channel. The French later sunk the ship.

7. Castillo de Bellver Oil Spill

When: Aug. 6, 1983 Where: Saldanha Bay, South AfricaAmount spilled: 79 million gallons

The Castillo de Bellver caught fire about 70 miles north west of Cape Town, and drifted in the open sea until it broke in two 25 miles off the coast. The ship’s stern sank along with the 31 million gallons of oil it was carrying. The bow section was towed and deliberately sunk later.

6. Nowruz Oil Field Spill

When: Feb. 10, 1983

Where: Persian Gulf, IranAmount spilled: 80 million gallons

The oil spill was the result of a tanker collision with an oil platform. The weakened platform was closed, and it collapsed upon impact, spewing oil into the Persian Gulf. The ongoing war between Iran and Iraq prevented the leak from being capped quickly.

5. Kolva River Oil Spill

When: Aug. 6, 1983

Where: Kolva River, RussiaAmount spilled: 84 million gallons

A poorly maintained pipeline caused this massive oil spill. The pipeline had been leaking for eight months, but a dike contained the oil until sudden cold weather caused the dike to collapse. Millions of gallons of accumulated oil were released that spread across 170 acres of streams, fragile bogs and marshland.

4. Atlantic Empress Oil Spill

When: July 19, 1979 Where: Off the coast of Trinidad and TobagoAmount spilled: 90 million gallons

This Greek oil tanker was caught in a tropical storm off the coast of Trinidad and Tobago when it collided with the Aegean Captain. The damaged ship started losing oil and continued to leak it into the ocean while it was towed. The oil tank finally sunk into deep water on Aug. 3, 1979, where the remaining cargo solidified.

3. Ixtoc 1 Oil Spill

Ixtoc I oil well blowout after the platform Sedco 135 burns and sinks in the Bay of Campeche, Mexico. Wikimedia Commons

When: June 3, 1979 Where: Bay of Campeche off Ciudad del Carmen, MexicoAmount spilled: 140 million gallons

Like the Gulf oil spill, this spill didn't involve a tanker, but rather an offshore oil well. Pemex, a state-owned Mexican petroleum company was drilling an oil well when a blowout occurred, the oil ignited and the drilling rig to collapse. Oil began gushing out of the well into the Gulf of Mexico at a rate of 10,000 to 30,000 barrels a day for almost an entire year before workers were finally able to cap the well.

2. Gulf oil spill

The Discoverer Enterprise and the Q4000 burn undesirable gases from the still uncapped Deepwater Horizon well in the Gulf of Mexico. DVIDSHUB /Wikimedia Commons

When: April 22, 2010Where: Gulf of MexicoAmount spilled: An estimated 206 million gallons

The Gulf oil spill is officially the largest accidental spill in world history. It began when an oil well a mile below the surface of the Gulf blew out, causing an explosion on BP’s Deepwater Horizon rig that killed 11 people. BP made several unsuccessful attempts to plug the well, but oil flowed — possibly at a rate as high as 2.5 million gallons a day — until the well was capped on July 15, 2010. Oil gushed from the broken well for more than 85 days, oiled 572 miles of Gulf shoreline, and killed hundreds of birds and marine life. The long-term effects of the oil and the 1.82 million gallons of dispersant used on this fragile ecosystem remain unknown, but experts say they could devastate the Gulf coast for years to come.

1. Arabian Gulf/Kuwait

When: Jan. 19, 1991

Where: Persian Gulf, KuwaitAmount spilled: 380-520 million gallons

The worst oil spill in history wasn't an accident — it was deliberate. During the Gulf War, Iraqi forces attempted to prevent American soldiers from landing by opening valves at an offshore oil terminal and dumping oil from tankers. The oil resulted in a 4-inch thick oil slick that spread across 4,000 square miles in the Persian Gulf.

How does the Exxon Valdez oil spill compare?

When the Exxon Valdez supertanker hit a reef off the Alaskan coast, 11 of its cargo tanks ruptured, dumping 11 million gallons of crude into Prince William Sound. But the spill could have been much worse — the Valdez was carrying 53 million gallons.

In terms of sheer volume, the Exxon Valdez spill ranks as the 36th worst oil spill in history; however, the spill was far from small. Despite attempts to use dispersing agents and oil skimming ships, oil washed onto 1,300 miles of Alaskan coastline. Today, oil remains a few inches below the surface on many of Alaska’s beaches.

Responders found carcasses of more than 35,000 birds and 1,000 sea otters, which was considered to be a fraction of the animal death toll because carcasses typically sink to the seabed. It’s estimated 250,000 seabirds, 2,800 sea otters, 300 harbor seals, 250 bald eagles, up to 22 killer whales died along with billions of salmon and herring eggs.

The repaired Exxon Valdez was renamed the SeaRiver Mediterranean, and, although it is banned from Alaskan waters, the tanker still carries oil around the world.

Catie Leary contributed to this story.