LONDON, June 4 (Reuters) - The BP (BP.L) Gulf of Mexico spill ranks as the worst in U.S. history.
As much as 19,000 barrels of oil (800,000 gallons or 3 million litres) a day has been flowing into the Gulf off the coast of Louisiana since the April 20 explosion, which sank the Deepwater Horizon offshore drilling rig and killed 11 crewmen.
But by a measure of absolute volume, Deepwater Horizon is not yet the world's largest spill.
The spill stands out for its proximity to U.S. shores and the publicity it has generated by comparison with other large, ongoing leaks in more remote parts of the world.
"This spill is in my view a game changer," said Lisa Speer, director of the Natural Resources Defense Council's international oceans programme in New York.
Estimates by a team of U.S. government and independent experts last week based on three separate methodologies and raw BP data showed that between 500,000 and 800,000 barrels had already leaked into the Gulf of Mexico.
That compares with up 3.5 million barrels spilled in 1979 by the Pemex-operated [PEMX.UL} Ixtoc offshore well over nine months.
"It compares to the Ixtoc. We're not there yet, but we could ultimately be looking at a spill that equates to or exceeds the Ixtoc," Speer said.
BP Chief Executive Officer Tony Hayward caused fury in the U.S. press when he suggested the Deepwater Horizon spill was relatively small [ID:nN02176649].
The following is a selection of some of the most significant oil spills, including marine leaks, pipeline leaks and oil dumping, in terms of severity and size across the globe.
Information has been compiled from Reuters and industry data bases and, where possible, figures have been converted into barrels per day from tonnes, gallons or cubic metres.
MARINE TANKER SPILLS
1979 - The Atlantic Empress and the Aegean Captain, two fully loaded oil tankers, collided 10 miles off the coast of Tobago in a tropical rainstorm, spilling more than 2,142,000 barrels of oil into the Caribbean.
1991 - The oil tanker ABT Summer exploded about 900 miles off the coast of Angola, spilling its entire cargo of 1,905,800 barrels at sea.
MARINE PLATFORM-OFFSHORE LEAKS/BLOWOUTS
1979 - The Pemex-operated Ixtoc I offshore well in Mexico's Campeche Bay blew out, spewing up to 3,500,000 barrels of crude oil over nine months in the worst offshore spill in North American history.
1969 - The Union Oil Platform A offshore well near Santa Barbara, California blew out, spilling up to 100,000 barrels of crude oil over 11 days and fouling the coastline, leading to broad opposition to offshore drilling and spurring the creation of the U.S. Environmental Protection Agency.
1977 - The Phillips Petroleum Ekofisk Bravo platform blew out for 8 days, releasing 202,381 barrels in the North Sea's biggest oil spill.
1983 - In the gulf off Iran a tanker struck a drilling platform, releasing some 1,904,000 barrels into the sea.
1988 - In the world's worst offshore accident for human casualties, the Piper Alpha oil platform exploded in the British sector of the North Sea, killing 167 people.
2001 - The Petrobras-operated P-36 offshore production facility exploded and collapsed into the sea off the coast of Rio de Janeiro, spilling some of the 10,000 barrels of fuel and crude it was storing.
2005 - A fire destroyed the ONGC-owned Mumbai High North processing platform off India's west coast, affecting 123,000 bpd of crude production, or 15 percent of the country's domestic output.
1991 - During the Gulf War, Iraqi forces opened valves and destroyed oil facilities in Kuwait, releasing about 12,376,000 barrels in the biggest oil spill in history.
MAJOR OIL COMPANY LEAKS
* Shell (RDSa.L) spilled around 110,000 barrels of oil around the world in 2009, with the lion's share coming from sabotage at their Odidi field in Nigeria and bomb explosions on the Trans Excravos pipeline and discharge, the company said on its website.
* Chevron (CVX.N) spilled around 9,300 barrels of oil on land and water in 2009, according to data available on its website.
* ExxonMobil (XOM.N) spilled around 18,000 barrels of hydrocarbons on land and water in 2009, according to date in its 2009 Corporate Citizenship Report.
* Total (TOTF.PA) said in its Environment and Society Report 2009 that it spilled 2,409 cubic metres of oil -- around 15,000 barrels -- last year.
* In May this year ExxonMobil declared force majeure on its Qua Iboe crude oil shipments at its Nigerian unit, affecting as much as 150,000 bpd after a leak was discovered on a key pipeline.
* In April this year a Chevron-operated pipeline leaked around 500 barrels of oil into the Delta National Wildlife Refuge in Louisiana.
* In January this year Royal Dutch Shell said it had shut three pumping stations after a key crude oil pipeline in the Niger Delta area of Nigeria was sabotaged, saying some oil had spilled into local creeks.
* In January this year Enbridge Energy Partners LP (EEP.N) shut down one leg of the main pipeline delivering Canadian crude to the United States after spilling around 3,000 barrels in North Dakota.
* In December last year, BP Plc said ice cracks caused a November leak in one if its Alaskan pipelines, spilling more than 1,000 barrels in the North Slope.
(Compiled by Chris Baldwin, edited by Jane Baird)