A growing oil spill in the Gulf of Mexico is expected to become one of the biggest oil-related environmental disasters in U.S. history and to lead to tougher oversight from regulatory authorities.
As a 120-mile (190-km) oil slick moves closer to the shoreline, a ruptured undersea well continues to spew some 5,000 barrels of crude oil a day, and it could be weeks to stop the flow.
Here is a look at some major oil spills that impacted the United States, some of which had regulatory repercussions. One spilled barrel holds 42 gallons.
March 2006 - Prudhoe Bay, Alaska
More than 5,000 barrels of oil spilled onshore on Alaska's North Slope due to a leak in a pipeline owned by BP. BP had to suspend production after it was discovered that pipeline corrosion caused the leak. The company was fined $20 million for negligence under the Clean Water Act. The incident led to stronger pipeline inspection requirements.
August-September 2005 - New Orleans, Louisiana
The Coast Guard estimated that more than 167,000 barrels of oil were spilled during Hurricane Katrina from various sources, including pipelines, storage tanks and industrial plants.
November 28, 2000 - Port Sulphur, Louisiana
Some 13,500 barrels of crude oil leaked into the Mississippi River about 60 miles south of New Orleans after the tanker Westchester lost power and ran aground. The spill was then the largest in U.S. waters since Exxon Valdez.
January 19, 1996 - Moonstone Beach, Rhode Island
Almost 20,000 barrels of home heating oil spread through the Block Island Sound when the tank barge North Cape and tug Scandia grounded after a fire started in the engine fire of the tug. The spill killed more than 10 million lobsters and prompted a ban on fishing in the area for several months.
August 10, 1993 - Tampa Bay, Florida
An estimated 8,000 barrels of oil carried by the Bouchard 155 spilled into Tampa Bay after the barge was in a collision with the freighter Balsa 37 and the barge Ocean 255.
June 8, 1990 - Galveston, Texas
The 886-foot Mega Borg released about 121,000 barrels of oil 60 miles off of Galveston after an explosion and subsequent fire in the pump room. The fire burned off much of the oil as it was lighter and more easily evaporated.
February 7, 1990 - Bolsa Chica State Beach, California.
The 811-foot American Trader tanker leaked some 7,100 barrels of crude into the ocean when its hull was punctured as it neared an oil pipeline mooring. An oil slick over 13 miles long harmed one of southern California's biggest nature reserves.
March 24, 1989 - Prince William Sound, Alaska
The tanker Exxon Valdez hit an undersea reef, spilling about 260,000 barrels of oil into the sea in the worst oil spill in U.S. history.
The U.S. Congress passed the Oil Pollution Act of 1990 in response to the spill, preventing any ship that had spilled more than 1 million gallons (23,800 barrels) of oil from operating in Prince William Sound. The legislation also phased in the double hull ship requirement, which a study said could have cut the size of the Exxon Valdez oil spill by 60 percent.
December 1976 - Buzzards Bay, Massachusetts
The Argo Merchant, a Liberian-registered oil tanker, ran aground southeast of Nantucket Island on December 15, 1976. Its crew was evacuated, but the ship's cargo -- some 183,000 barrels of fuel oil -- could not be offloaded. Six days later, the ship broke apart, spilling all of the fuel, enough to heat 18,000 homes for a year.
January 1969 - Santa Barbara, California
A blowout on a Union Oil Co drilling rig six miles off the coast of Summerland, California, forced some 80,000 barrels of crude oil into the Santa Barbara Channel. An 800-square-mile slick damaged 35 miles of coastline and killed thousands of sea animals and birds.
The oil spill has been considered the catalyst of the U.S. environmental movement and spurred a moratorium on offshore drilling which was ended by President George W. Bush and by U.S. Congress in 2008.
(Compiled by Jasmin Melvin and Tom Doggett)