The SPILL: What happens in a spill?

Oil spills: Definition & causes

Oil spills conjure up images of blackened, oil-tainted waters and beaches, dead and dying fishes and oil-coated sea birds. Throughout history, oil spills have disrupted the beauty of the environment, costs billions of dollars in cleanup and remediationremoval of pollution from the environment to remove risks to human health and the ecology of an area and caused the suffering and death of countless species of wildlife. Oils spills may also have long-term impacts on the environment by disrupting the food chainshows how living things get food and how nutrients (energy) are passed from living thing to another.

An oil spill is the release of a liquid petroleum product such as crude oil, refined petroleum such as gasoline, or diesel fuel into the environment. Although most oil spills are the result of human activities, some result from natural causes. The most newsworthy oil spills have occurred in the marinerelating to the oceans or seas environment, but oil spills occur in rivers, deserts, and other environments, too.

Manmade Disasters Spill Oil

Many oil spills are a result of human activities. Those that occur in the earth’s waterways tend to draw the most attention and send more than 300 million gallons of oil into North American waters every decade. This amount is roughly double the highest estimate of the BP spill (Deepwater Horizon), according to studies by some of the world's top scientists. However, most human-related spills are on land.

Listed here are some ways that oil spills occur:

burning oil fields in Kuwait

Oil wells burning in Kuwait during Operation Desert Storm. Source: U.S. Army Corps of Engineers, Credit: Jonas Jordan


diagram of an oil seep from the ground

Some oils leaks to the surface from areas lodged between geologic layers. Source: Origin of Petroleum, Credit: Lecture of Jamie Toro

Nature Spills Oil, Too

A natural petroleum seep is a place where liquid or gaseous hydrocarbons escape to the ground surface or the ocean floor. The seepage comes from buried oil and gas accumulations which escapes through fractures in the earth’s rocks or directly from rock outcrops. When the oil industry was just beginning, these natural seeps were the first tools used to locate new oil resources before scientists and geologists developed sophisticated sensors.

two types of natural seeps

(Left) Petroleum seep near the Korňa in northern Slovakia. Source: Wikipedia
(Right) Oily outcrop in California. Source: Wikipedia

The exact effects and size of natural oil seeps in the oceans are unknown, but we do know that contamination caused by natural seeps is far greater than contamination caused by manmade events.

The National Research Council (NRC), of the U.S. National Academy of Sciences, maintains that "natural oil seeps contribute the highest amount of oil to the marine environment, accounting for 46% of the annual load to the world's oceans." Submarines and remote sensing are used to discover and study the effects of these natural seeps.

pie charts showing the sources of oil in marine environments

Pie charts from the Oil in the Sea, National Academy Sciences, 2002

quizWhat percentage of petroleum in North American Marine Waters comes from natural seeps?


In additional to the submarines and remote sensing tools, scientists use satellite images of the ocean to detect oil seeps and spills. Check out the NASA images that were taken in May 2006. The left image is a wide-area view of the central Gulf of Mexico below southeast Louisiana. The white square surrounds several natural oil seeps. The right image is a close-up view of this square, showing dozens of natural crude oil seeps in the deep water of the central Gulf.

satellite images of oil seeps

Satellite images of oil seeps in the Gulf of Mexico, Source: NASA, May 13, 2006

Where does all this oil go? Some of the oil washes on shore as tar balls and massive oil slicks may be seen at times, as previously shown in the NASA images. Much of the oil is heavy and tends to sink back down to the ocean floor creating an oil fallout shadow that contaminates ocean floor sediments (see figure). Researchers have sampled around the seeps and found that microbesan organism that is microscopic; too small to be seen with the naked eye degrade most of the oil.

diagram explaining cycle of oil seeping naturally in the ocean

Naturally seeping oil in the ocean. Source: Woods Hole Oceanographic Institution, Credit: Jack Cook

This illustration shows the route traveled by oil leaving the subseafloor reservoir as it travels through the water column to the surface, and ultimately falls back to the seafloor. The oil remaining after weathering and microbial degradation falls in a plume shape onto the seafloor where it remains in the sediment.

History of spills

map of Alaska showing oil spill from Exxon tanker

A map of Alaska. The green area depicts the extent of oil spill coverage from the Exxon Valdez. Source: Alaska Dept of Natural Resources

Prior to the Deepwater Horizon oil spill, the most notable oil spill in the U.S. was the Exxon Valdez incident that occurred on March 24, 1989 in Prince William Sound, Alaska.

The oil tanker the Exxon Valdez grounded on Bligh Reef releasing nearly 11 million gallons of crude oil from a ruptured hull into Prudhoe Bay. In the weeks that followed, the crude oil spread over a wide area of the Sound causing much destruction in this biologically important environment.

Mortality of marine animals such as harbor seals, killer whales, sea lions and sea otters occurred. Bald eagles, black-oyster catchers, common murres, Harlequin ducks and Marbled Murrelets were among the bird populations that suffered. Pink salmon and Pacific herring were among the fish populations that took years to repopulate. This incident was the largest single oil spill in the coastal waters of the United States prior to the Spring 2010.

alaskan animals, an otter and a sea lion

(Left) Up to 5,000 sea otter died in the Exxon Valdez oil spill. Otters feed in the intertidal zones and, therefore, may still be negatively affected by oil residues. Source: U.S. Fish & Wildlife Service, Credit: David Menke.
(Right) The Steller Sea Lions were adversely affected by the oil spill. The western populations are an endangered species, in danger of becoming extinct. Source: National Marine Mammal Library

The incident caught Exxon as well as government organizations unprepared and slow in response. Although tragic, the Valdez incident awakened people as well as the government about the serious threat of oil spills. It also served as a lesson in cleaning up the environment during and after a spill.

The cleanup effort cost Exxon $2.5 billion alone, and Exxon was forced to pay over $1.1 billion in miscellaneous settlements. In addition, a 1994 federal jury also fined Exxon an additional $5 billion for recklessness. Exxon later appealed this decision. Exxon's image was tarnished as a result of the incident as angry customers cut up their Exxon credit cards and others boycotted Exxon products.

Learn more about the most devastating oil spills in history.

quizStudy the following map that shows 10 big oil spills. Rollover each number to learn about the spills. The Deepwater Horizon is the worst spill in U.S. history. How does it compare with two other spills found on this map?

map of ten big spills

Louisiana leads in spills

map of Louisiana oil and gas resources

Map showing the oil infrastructure in Louisiana. Source: Louisiana Dept of Natural Resources

Unfortunately, Louisiana often leads the United States in oil spills. This trend is due to several reasons:

As a result, the economy and ecology of the state are deeply impacted.

Broken Pipelines & Spills

The Coast Guard released these pictures of an oil leak in National Wildlife Refuge in early April 2010. Over 18,000 gallons of oil leaked from the main pipeline before the pipeline operator, Chevron Pipe Line Company, could close the broken section. The Coast Guard worked with staff from the Louisiana Oil Spill Coordinator’s Office to minimize the environmental impact of the spill.

U.S. Coast guard sampling oiled water

(Left) Taking a sample of the 18,000 gallons spilled from a broken pipeline. Source: U.S. Coast Guard, Credit: Jesse Kavanaugh
(Right) Oil spilled near the Delta National Wildlife Refuge. Source: U.S. Coast Guard, Credit: Jesse Kavanaugh

Hurricanes & Spills

Hurricanes Katrina, Rita, and Gustav were responsible for a number of oil spills in Louisiana. Forty-four oil spills were reported from hurricane Katrina. Some of the spills were relatively small (only a few hundred gallons), but one spill released nearly 4 million gallons. In fact, it is estimated that the oil spills in Louisiana after Katrina amounted to two-thirds the amount of oil spilled by the Exxon Valdez. Fortunately the spills occurred over a broad area and were not concentrated in a small area like the Valdez incident.

tanker and spill radius from murphy spill site after Katrina

(Left) Damaged oil tank after Katrina, Source: U.S. Coast Guard. (Right) These damaged containers resulted in the Murphy Oil Spill in Chalmette, LA, Source: Environmental Protection Agency, 2005

animation of Exxon Valdez oil spill

This NOAA animation shows how the oil spread after the Exxon Valdez spill.

whose job?

The Enviornmental Protection Agency (EPA) serves as the lead agency for oil spills occurring in inland waters in the United States. The U.S. Coast Guard and the National Oceanic and Atmospheric Administration (NOAA) handle all spills in coastal waters and deep ports, like those surrounding Louisiana.

damaged tanker

did you know?

Approximately 20 to 25 tons of oil have leaked from the seafloor each day for the last several hundred thousand years.

methane bubbles to ocean surface

Source: LiveScience, Credit: Dave Valentine, University of California at Santa Barbara

This photograph shows oil and methane bubbling to the ocean's surface from the world’s largest natural seep in Coal Oil Point, California.

spill talley

Between 1990 and 1999, an average of 150,000 tons of oil spilled each year into the world's waterways [source: National Academies].

This amount equals 44 million gallons or enough oil to fill 68 olympic-sized swimming pools.

the really bad

2001 was a particularly bad year, with five spills occurring within the same week [source: Mariner Group].

small spill map

Map designed by Lasting News. No longer online.

katrina spills

Did you know that Hurricane Katrina was responsible for more than 44 oil spills in Louisiana? Check out this damaged platform.

damaged platform

Damaged oil rig being towed in for repairs after Hurricane Katrina. Modified from: flickr, Credit: Kevin (iapetus)

LA spills

Learn more about the history of oil spills in Louisiana in this Advocate article.

The Louisiana Oil Spill Coordinator's Office (LOSCO) is responsible for tracking spills.

First visit the LOSCO website. Then browse their records. They have everything from maps of abandoned vessels and spills to locations approved for chemical dispersants that would be used to clean up a spill.

animal experts

The U.S. Fish & Wildlife Service has a team of scientists devoted to studying and rescuing animals from environmental contamination.

They review permits, causes, and effects to protect fish and wildlife from oil pollution, hazardous waste, industrial and agricultural run-off, and pesticides. Learn more about the Environmental Contaminants Program.

Tundra swan in Idaho

Source: U.S. Fish & Wildlife Service, Credit: Brian Spears