Update: According to new estimates released on Aug. 2, 2010, more than 172 gallons of oil spilled into the Gulf of Mexico between April and July 15. This makes it the largest accidental spill of all time, though still likely smaller than the intentionally-caused Gulf War spill. 

 If current estimates for the Deepwater Horizon oil leak in the Gulf of Mexico are correct, the massive spill could eventually dwarf that of Exxon Valdez spill of 1989 -- previously the largest in U.S. history -- by as much as three times. At a rate of 5,000 barrels a day, for an estimated 90 days, well over 20 million gallons of crude could be pumped out onto the Louisiana coastline. Even then, it might only crack the top 15 largest oil spills in world history. Here are the top five.

GULF WAR

Location: Persian Gulf

Date: Jan. 21, 1991

Amount: Between 160 million and 420 million gallons

How it happened: As Iraqi forces withdrew from their position in Kuwait, they sabotaged hundreds of wells, oil terminals, and tankers. All told, a minimum of 4 million barrels were poured into the Persian Gulf. Within a couple of years however, experts happily reported that the biggest oil spill in history had a surprisingly small environmental impact.

THE IXTOC 1 OIL WELL

Location: Gulf of Mexico

Date: June 3, 1979 - March 23, 1980

Amount: 138 million gallons

How it happened: This exploratory oil well suffered a catastrophic blowout (whereby pressure causes the well to explode), caught fire, and caused the drilling platform to collapse. For months, 10,000 to 30,000 barrels of oil gushed into the ocean every day.

ATLANTIC EMPRESS/AEGEAN CAPTAIN COLLISION

Location: Trinidad and Tobago

Date: July 19, 1979

Amount: 90 million gallons

How it happened: Two fully loaded oil carriers, the Atlantic Empress and the Aegean Captain, collided 10 miles off the coast of Trinidad and Tobago during a tropical rainstorm. Both ships caught fire and began leaking their contents in what would become the largest tanker-based spill ever recorded.

NOWRUZ PLATFORM

Location: Persian Gulf

Date: February 4, 1983 - September 18, 1983

Amount: 80 million gallons

How it happened: During the height of the Iran-Iraq War, an oil tanker hit the Nowruz Field Platform in the gulf and knocked it onto a 45 degree angle, damaging the well underneath. The resulting leak of 1,500 barrels a day could not be capped for months because the platform was under constant attack by Iraqi planes.

ABT SUMMER

Location: Off the coast of Angola

Date: May 28, 1991

Amount: 80 million gallons

The ABT Summer, a tanker holding 260,000 tons of crude, suffered an explosion 900 miles off the coast of Angola. It burned for three days before sinking and was never recovered. Luckily, high seas dispersed the oil and dulled its potential environmental impact.