An oil drilling platform in oil-free water two years after the Deepwater Horizon oil spill in the Gulf of Mexico. Credit: Terese Collins, On Wings Of Care

Gulf Oil Spill


by The Ocean Portal Team

The Gulf oil spill is recognized as the worst oil spill in U.S. history. Within days of the April 20, 2010 explosion and sinking of the Deepwater Horizon oil rig in the Gulf of Mexico that killed 11 people, underwater cameras revealed the BP pipe was leaking oil and gas on the ocean floor about 42 miles off the coast of Louisiana. By the time the well was capped on July 15, 2010 (87 days later), an estimated 3.19 million barrels of oil had leaked into the Gulf.

The well was located over 5,000 feet beneath the water’s surface in the vast frontier of the deep sea—a permanently dark environment, marked by constantly cold temperatures just above freezing and extremely high pressures. Scientists divide the ocean into at least three zones, and the deep ocean accounts for about three-quarters of Earth’s total ocean volume.

Immediately after the explosion, workers from BP and Transocean (owner of the Deepwater Horizon rig), and many government agencies tried to control the spread of the oil to beaches and other coastal ecosystems using floating booms to contain surface oil and chemical oil dispersants to break it down underwater. Additionally, numerous scientists and researchers descended upon the Gulf region to gather data. Researchers are still trying to understand the spill and its impact on marine life, the Gulf coast, and human communities.

You can explore the spill in our interactive and read on for more information.







The Spill

The Oil's Spread

Mark Dodd, a wildlife biologist from Georgia's Department of Natural Resources, surveying oiled sargassum seaweed in the Gulf of Mexico after the Deepwater Horizon oil spill in 2010.
Mark Dodd, a wildlife biologist from Georgia's Department of Natural Resources, surveying oiled sargassum seaweed in the Gulf of Mexico after the Deepwater Horizon oil spill in 2010. (Georgia Department of Natural Resources)

Over the course of 87 days, the damaged Macondo wellhead, located around 5,000 feet beneath the ocean's surface, leaked an estimated 3.19 million barrels (over 130 million gallons) of oil into the Gulf of Mexico—making the spill the largest accidental ocean spill in history.

Once the oil left the well, it spread throughout the water column. Some floated to the ocean's surface to form oil slicks, which can spread more quickly by being pushed by winds. Some hovered suspended in the midwater after rising from the wellhead like a chimney and forming several layers of oil, dispersant and seawater mixtures drifting down current; during the spill a 22-mile long oil plume was reported. This plume formed because chemical dispersants, released into the water to break up the oil so it could wash away, allowed the oil to mix with seawater and stay suspended below the surface. And some oil sunk to the seafloor by gluing together falling particles in the water such as bacteria and phytoplankton to form marine snow. As much as 20 percent of the spilled oil may have ended up on top of and in the seafloor, damaging deep sea corals and potentially damaging other ecosystems that are unseen at the surface.

You can explore where the oil went in our interactive.

Clean-up Methods

Physical Methods

Pelicans gather at the Deepwater Horizon oil spill.
GRAND ISLE, La. -- Brown pelicans congregate on containment boom that surrounds Queen Bess Island, a few miles north of Grand Isle, La. August 25, 2010. The island is a sensitive nesting area for brown pelicans. More about the Gulf oil spill can be found in our Gulf oil spill featured story. (Petty Officer 3rd Class Cory J. Mendenhall, U.S. Coast Guard)

When oil spills into the ocean, it is difficult to clean up. When you have 3.19 million barrels to clean up, it is even harder.

Part of the difficulty is that no two spills are alike. The amount and type of oil (whether crude or refined) affects how it spreads, and a spill in seawater spreads differently than freshwater. Local environmental conditions also play a huge role: currents, tides, weather, wind speed and direction, air temperature, water temperature and presence of ice all affect how the oil spreads and how well cleanup workers can access the spill area. This variability makes it difficult to plan for spills ahead of time.

The most basic method of clean up is to control the spread of the oil using physical barriers. When oil spills in water, it tends to float to the surface and spread out, forming a thin slick just a few millimeters thick. (A very thin slick is called a sheen, which often looks like a rainbow and can be seen in parking lots after a rainstorm.) Cleanup workers first surround the slick with floating booms to keep it from spreading to harbors, beaches or biologically important areas like marshes. Then they can use different tools to remove the collected oil. Often they will drive skimmers, boats that skim spilled water from the water's surface, through the slick. 

After most of the oil is removed by skimmers, workers use sorbents to mop up the trace amounts left behind. Sorbents either absorb oil like a sponge or adsorb oil, which means that oil sticks to its surface. They come in three main types: natural organic materials like peat moss, straw, hay and sawdust; natural inorganic materials like clay, volcanic ash, sand, or vermiculite; and synthetic sorbents made of materials similar to plastic like polyurethane, polypropylene, and polyethylene. Which type is used will depend on the particular spill, as some types of sorbents work best on different types of oil and under different weather conditions.

Another option is to speed up the oil's natural biodegradation using dispersants. (See next section.)


A C-130 Hercules from the Air Force Reserve Command deploys dispersant into the Gulf of Mexico May 5, 2010, as part of the Deepwater Horizon/BP oil spill response effort.
A C-130 Hercules from the Air Force Reserve Command deploys dispersant into the Gulf of Mexico May 5, 2010, as part of the Deepwater Horizon/BP oil spill response effort. (U.S. Air Force, Tech. Sgt. Adrian Cadiz)

Removing spilled oil from the environment is a difficult task. Because oil is hydrophobic (doesn't mix with water), it floats to the surface when it spills into the ocean and forms large slicks. These slicks can wreak havoc on coastal ecosystems and animals, so cleanup workers use dispersants—chemicals that break down the oil into smaller particles that mix with water more easily—to prevent them from forming. Evaporation and bacteria can then degrade these tiny droplets more quickly than if they were in a large slick, or waves can wash them away from the spill site.

Dispersants are often used when workers want to stop the slick from spreading to a protected area like a harbor or marsh. This can be a boon for animals found on the surface and coast, such as seabirds, marine mammals and those found in the Gulf’s mangroves, because the oil is moved out of their habitat. But dispersants can also enter the food chain and potentially harm wildlife.

In the case of the Deepwater Horizon oil spill, clean-up workers treated the oil with over 1.4 million gallons of various chemical dispersants. Typically such large amounts are sprayed over the open ocean from an airplane or helicopter. But during the BP oil spill, they were also injected straight into the Macondo wellhead, the source of the leak, in order to reduce the amount of oil that reached the ocean surface. Five years after the spill some scientists believe that injecting dispersants directly at the wellhead may not have done much to help reduce the size of the oil droplets. 

Just because the oil and dispersants are out of human sight and mind in the deep sea doesn't mean they're gone. It's possible that life in the deep sea was exposed to the dispersant-oil mixture. Scientists have found that the dispersant-oil mixture was rapidly colonized and broken down by bacteria that sunk towards the bottom. Any bits of the mixture that didn't get broken down would then get buried in coastal and deep-sea sediments, where its breakdown slows.

While the dispersant helps expose more of the oil to bacteria and waves which help to break it down, it also makes the oil more available to wildlife. One 2012 study showed that the combination of oil and the dispersant Corexit is 3 to 52-times more toxic to rotifers (microscopic animals) than oil by itself. This isn't because of anything inherently dangerous in the mixture of the two; the rotifers are more able to ingest oil once it's made accessible by the dispersant. But overall, scientists have concluded that the amount of oil determines whether or not adding dispersant is toxic or not, and the oil concentrations during the Deepwater Horizon oil spill were well below toxic levels. Furthermore, oil slicks in and of themselves are toxic to marine wildlife, and this must be taken into consideration when choosing to use dispersants. 

There is still more research needed to understand the effects of dispersant. A modeling effort supported by the Gulf of Mexico Research Initiative offered evidence that the dispersants injected into the Macondo wellhead may not have helped to lessen the amount of oil reaching the surface after all.

A lot of research is still needed to fully understand the long-term effects of dispersants on the region and its inhabitants—not to mention how they move through the food chain to impact larger predators, such as people. Researchers are developing new dispersants that cause less environmental damage for the next spill. (See "Human Health Impacts.")

Ecosystem Effects

Effects on Wildlife

Dolphins swimming among oily patches in the Gulf of Mexico
Striped dolphins swim among emulsified oil patches on April 29, 2010 in the Gulf of Mexico, a few days after the Deepwater Horizon oil spill. (NOAA)

There were some immediate impacts to the animals of the Gulf of Mexico that could be seen with the naked eye: pelicans black with oil, fish belly-up in brown sludge, smothered turtles washed up on beaches. But not much time has passed since the spill, and it will take many more years of monitoring and research to understand what happened. 

Strandings of both dolphins and sea turtles increased significantly in the years following the spill. "From 2002 to 2009, the Gulf averaged 63 dolphin deaths a year. That rose to 125 in the seven months after the spill in 2010 and 335 in all of 2011, averaging more than 200 a year since April 2010," reported Reuters in 2015. Since then, dolphin deaths have declined, and long-term impacts on the population are not yet known. Kemp's ridley sea turtle nests have gone down in the years since the spill, and long-term effects are not yet known.

Seabirds were initially harmed by crude surface oil—even a small bit of oil on their feathers impeded their ability to fly, swim and find food by diving. Seabird losses may have numbered in the hundreds of thousands, but reliable estimates are hard to come by. Looking beyond the sea, researchers are currently studying how oil may have affected land birds that live in the marshes along the Gulf coast.

Invertebrates in the Gulf were hard hit by the Deepwater Horizon spill—both in coastal areas and in the deep. Shrimp fisheries were closed for much of the year following the spill, but these commercially-important species now seem to have recovered. Deep-water corals grow very slowly and can live for many centuries. Found as deep as 4,000 feet below the surface, corals near the blowout showed signs of tissue damage and were covered by an unknown brown substance, later identified as oil from the spill. Laboratory studies conducted with coral species showed that coral larva exposed to oil and dispersant had lower survival rates and difficulty settling on a hard surface to grow.

The impact of the spill on fish communities is still largely unknown. Lab studies have shown that oil can cause heart defects in the developing larvae of bluefin tuna and other fish, but we won't know if this occurred in the wild until after those larvae would have grown up. Some fish larvae populations actually grew after the spill, as they had more food in the form of oil-eating microbes. 

There were some reports of deformed wildlife after the spill. For years following the spill there were reports of fish with lesions and deformities, and some reports of eyeless and deformed shrimp after the spill. However, consuming Gulf seafood is now completely safe.

Over 1,000 miles of shoreline on the Gulf of Mexico, from Texas to Florida, was impacted by oil from the Deepwater Horizon blowout. Much of this area has been cleaned, but eroded shorelines are taking longer to recover and erosion rates have accelerated in these areas. 

You can explore more ecosystem effects in our interactive.

Where Did the Oil Go?

Underwater Robot

An autonomous underwater vehicle from the Monterey Bay Aquarium Research Institute (MBARI) being launched from the NOAA Ship Gordon Gunter in the Gulf of Mexico.
An autonomous underwater vehicle from the Monterey Bay Aquarium Research Institute (MBARI) being launched from the NOAA Ship Gordon Gunter in the Gulf of Mexico. (Yanwu Zhang © 2010 MBARI)

In May 2010, the Monterey Bay Aquarium Research Institute (MBARI) sent a high-tech robotic submersible to the oily waters of the Gulf of Mexico. Like other autonomous underwater vehicles (AUV), the robotic sub was programmed at the surface to navigate through the water on its own, collecting information on deep oil plumes from the Deepwater Horizon spill as it traveled. Although satellites and aircraft helped show the extent of the spill at the surface, researchers hoped that the AUV would allow them understand what was happening farther down in the water column.

During the NOAA-sponsored expedition, MBARI's AUV mapped part of a plume 1,000 meters (3,300 feet) below the surface, and collected water samples at various depths. The resulting data helped the researchers identify a persistent deep oil plume and link the oil in this plume to its source: the Deepwater Horizon blowout.

Modeling the Movement

Drifters deployed into the Gulf of Mexico sent location information back to scientists through a GPS satellite. Some of the 5.7 million data points about the drifters locations are seen in this map of the Gulf.
Drifters deployed into the Gulf of Mexico sent location information back to scientists through a GPS satellite. Some of the 5.7 million data points about the drifters locations are seen in this map of the Gulf. (Photo courtesy of CARTHE)

Once the over 200 million gallons of oil began spewing out of the damaged wellhead—where did it go? Keeping track of that much oil—especially as it sinks into the deep sea—is a difficult task that can't be done with eyes alone. Along with visual tracking, computer models of the oil's movement helped researchers get a better sense of what path it took and where it ended up. 

To build the models, researchers first had to understand where ocean eddies, currents and waves carried the tiny oil particles. To understand surface water movement better, researchers set small, yellow boards made of wood afloat on the ocean's surface and asked beachgoers to report where they found these “drift cards” when they washed up on shore. This citizen scientist endeavor provided general information about how far the waves can carry a floating object and specific data points that can be used to improve models of where the oil disperses. 

Further data collection has been ongoing since the spill by the Consortium for Advanced Research on Transport of Hydrocarbon in the Environment (CARTHE). CARTHE has more high-tech "drift cards:" their “drifters” are small buoy-like instruments with GPS, which ping their locations to satellites as they drift on ocean currents. Their location gets tracked for weeks or months at a time and provide an unprecedented amount of location-based data for modeling. This information can be used to better predict oil movement in case of future spills.

This image is a helper image for making the video responsive.
A Waterlust & CARTHE film

Absorbed into the Ecosystem

An environmental chemist collects samples of oil in the Gulf of Mexico from the Deepwater Horizon spill. The resulting chemical “fingerprint” of the oil will help determine the origin of other samples.
An environmental chemist collects samples of oil in the Gulf of Mexico from the Deepwater Horizon spill. The resulting chemical “fingerprint” of the oil will help determine the origin of other samples. (J. Short, Oceana, and S. Senner, Ocean Conservancy)

After the Deepwater Horizon spill, oil was mixed throughout the ocean and made its way to coastal and deep-sea sediments. Researchers continue to collect samples from both the water and the sediment to determine if oil is present, and where exactly it came from. Chemical analysis of oil found after a spill can be used to determine its original source. In the case of Deepwater Horizon, tracking the origins of oil slicks that appeared after the well was capped proved helpful in determining if a new leak might have sprung.

Gulf of Mexico Research Initiative

Research Projects

One-meter-tall plastic drifters are released into the Gulf of Mexico in 2012. Over 300 of these drifters were released and their location information was sent to researchers every five minutes through GPS satellite.
One-meter-tall plastic drifters are released into the Gulf of Mexico in 2012. Over 300 of these drifters were released and their location information was sent to researchers every five minutes through GPS satellite. (Photo courtesy of CARTHE)

About a month after the Deepwater Horizon oil spill (while the oil was still leaking out of the Macondo wellhead) BP announced that they would provide $500 million to fund an independent research program that would study the impacts of the spill on the environment and public health. With this funding, the Gulf of Mexico Research Initiative (GoMRI) was formed as a 10-year independent research program. The GoMRI research board, which is independent from BP, makes funding and research decisions, and as of early 2014 over $175 million has been distributed to research institutions, many of which are located in Gulf states. 

At the outset, the twenty-person GoMRI board adopted five main research themes to focus on: physical movement of the oil and dispersant, degradation of the oil and its interaction with the ecosystem, environmental effects of the oil and dispersant, development of technology for improved response and remediation, and the effects of oil and dispersant on human health. GoMRI funded studies have examined where the oil went after the spill, and how the oil affected many types of marine life, including deep-sea coral ecosystems, seabirds, and jellyfish, to name just a few.

Read more about GoMRI research:



Smithsonian holdings may show oil's impact in Gulf

Photo collage of six species of invertebrates.
The Smithsonian's Department of Invertebrate Zoology has a collection of over 57,000 specimens from over 5,700 sites in the Gulf of Mexico, which are now catalogued on Google Earth (Smithsonian Institution NMNH Department of Invertebrate Zoology)

As scientists in the Gulf collect organisms potentially affected by the oil, they will need to compare them to animals from previous decades to identify how they have changed, if at all.

Here's where Smithsonian Collections can play a role. Soon after the Deepwater Horizon oil spill, Smithsonian Collections staff plotted invertebrate holdings from the Gulf onto Google Earth. Since 1979, invertebrate specimens have been deposited  in the national collections of the National Museum of Natural History's Department of Invertebrate Zoology. In the Gulf of Mexico, more than 57,000 invertebrates (points on the map) from 5,789 distinct collecting sites from 14 Mineral Management Service survey programs (point colors) have been cataloged.

Following the Deepwater Horizon incident in late April 2010, collections staff updated the files to reflect the latest areas affected by the spill in real-time. “The points on the map represent less than half of our Gulf of Mexico holdings, the rest—approximately 75,000—still need to be processed and cataloged,” said Bill Moser, museum specialist.

Oil Spill Lessons from Panama

Marine Ecologist Jeremy Jackson
Marine ecologist Dr. Jeremy Jackson and a team of researchers conducted an in-depth study of the effects of a 1986 oil spill on the coast of Panama. (Smithsonian Ocean Portal)

A Smithsonian study of a 1986 oil spill on the coast of Panama attracted renewed interest for its insights into the effects of oil spills on coastal systems. Working with the Smithsonian Tropical Research Institute, marine ecologist Dr. Jeremy Jackson and a team of researchers examined the spill’s immediate and long-term effects on the coast in Bahia las Minas, Panama.

The benchmark study (PDF), published in 1989, documented the damage oil causes to coastal and tidal habitats. It's particularly notable because it includes 15 years of ecological data about the area before the spill collected by the Smithsonian. The affected area includes the Smithsonian biological reserve known as the Galeta Marine Laboratory. “What we learned, in a nutshell, was never, ever, ever, ever allow oil to get into a complex coastal system of mangrovessea grasses, and coral reefs because you’ll never get it out,” said Dr. Jackson.

In this video interview with the Smithsonian Ocean Portal, he reflects on the Panama study and its implications for the Gulf oil spill, and reminds listeners that the greatest threats to the ocean—overfishingclimate change, and other types of pollution—combined actually exceed the devastation that unfolded in the Gulf of Mexico oil spill. “If there’s any silver lining in the [Gulf] oil spill,” he said, “it’s that it might make us wake up to the magnitude of what we’re dealing with.” 

Featured Scientist

Dr. Chris Reddy, Marine Chemist

Dr. Chris Reddy, an environmental chemist from Woods Hole Oceanographic Institution, studies oil spills and their long-term impacts.
Dr. Chris Reddy, an environmental chemist from Woods Hole Oceanographic Institution, studies oil spills and their long-term impacts. (History Channel & Smithsonian Institution)

At Woods Hole Oceanographic Institution in Massachusetts, Chris Reddy studies the long-term effects of oil spills, as well as natural oil seeps that occur off the coast of Santa Barbara, California. In this video, watch as he digs beneath the surface in Wild Harbor salt marsh in Cape Cod, Massachusetts to find layers of oil from a spill that occurred more than 40 years ago. This leftover oil continues to impact the wetland's ecology and wildlife. “When this spill first occurred in 1969, about a month after I was born, people thought that it would only last a week,” he says. And to the naked eye, the marsh looks beautiful and pristine. But oil has persisted in the sediments and continues to adversely affect the marsh’s mussels, crabs, and grasses. “Oil can last for a long time and has a lot of biological impact.” In June 2010, Dr. Reddy testified before a Congressional panel investigating the Gulf oil spill.

Threats & Solutions

Human Health Risks

Workers contracted by BP load oily waste onto a trailer on Elmer's Island, just west of Grand Isle, La., May 21, 2010.
Workers contracted by BP load oily waste onto a trailer on Elmer's Island, just west of Grand Isle, La., May 21, 2010. (U.S. Coast Guard photo by Petty Officer 3rd Class Patrick Kelley)

In the immediate aftermath of the Deepwater Horizon oil spill, concerns about public health focused on people coming into direct contact with the oil and dispersants. The Centers for Disease Control and Prevention offered safety advice to Gulf Coast residents and relief workers and the EPA conducted toxicity tests on dispersants. A recent study discovered dispersants had an unintended benefit during the initial oil cleanup. As the dispersant broke apart the oil into smaller droplets it also decreased the amount of harmful gases that rose to the sea surface where emergency cleanup crews were working. This decreased the health risks associated with working near the spill, reduced the number of days where it was too hazardous to work, and enabled a quicker cleanup. However, long-term questions about oil spills and their impact on human health remain. The National Institutes of Health began to address these in a study that is tracking 33,000 cleanup workers and volunteers for a decade. The research will assess whether exposure to crude oil and dispersants has an effect on physical and mental health.

As the days, weeks, and months progressed the indirect impacts related to seafood consumption also gained attention. The chemicals in oil that are of most concern to humans are called polycyclic aromatic hydrocarbons (PAHs). Some of these are known to cause cancer. The U.S. Food and Drug Administration is charged with monitoring the levels of PAHs in Gulf Coast seafood. It works in conjunction with NOAA, the EPA, and state agencies to determine which fisheries are safe to open and which ones should be closed. In order for a fishery to be reopened, it must pass both a "smell" test and a chemical analysis. Seafood cannot go to market if it contains harmful levels of PAHs or if it emits an odor associated with petroleum or dispersants. Fishing area closures peaked on June 2, 2010, when 88,522 square miles of the Gulf of Mexico were off-limits. On April 19, 2011, NOAA announced that commercial and recreational fishing could resume in all of the federal waters that were affected by the spill.

Nine years after the spill, the National Academies of Science determined that dispersant impacts on seafood were extremely low, citing studies that found dispersant chemical concentrations to be low or nonexistent in fish and shellfish.

Rescuing Animals in the Oil Spill

A young Kemp's ridley sea turtle in recovery.
One of many Kemp’s ridley sea turtles (Lepidochelys kempii) recovering at the Audubon Aquarium of the Americas, after the 2010 Gulf of Mexico oil spill. Turtles were cleaned and nursed back to health with the help of New England Aquarium staff. (New England Aquarium)

Pictures of pelicans, sea turtles, and other Gulf of Mexico wildlife struggling in oil were among some of the most disturbing images of the Deepwater Horizon oil spill disaster in 2010. According to the U.S. Fish and Wildlife Service, thousands of “visibly” oiled animals (pdf) —which include birds, sea turtles, and marine mammals—were collected by authorities in the vicinity of the Deepwater Horizon oil spill. Many of the animals were already dead, but for those found alive, dozens of organizations, including the Smithsonian’s National Zoological Park and the New England Aquarium (NEA), were mobilized to rescue, rehabilitate, and later release animals affected by the spill. National Zoo personnel were dispatched to the Gulf largely to assist with the process of relocating animals affected by the spill and helping to identify future release sites for those rescued. Dr. Luis Padilla, a Zoo veterinarian who helped with a pelican release in Texas, and Dr. Judilee Marrow were among those who assisted in the Gulf.

NEA staff who helped to rehabilitate sea turtles rescued from the Gulf oil spill offered a behind-the-scenes view on the aquarium’s Marine Animal Rescue Team Blog. The blog described how rescuers in boats and spotter planes were “looking for rounded mounds on the surface of the oil, which usually means that there is a turtle floating under the surface of the oil." The rescue team, based at the Audubon Aquarium of the Americas in New Orleans, treated dozens of endangered sea turtles, such as Kemp's ridley, loggerheads, green sea turtles, and hawksbills. To learn more about how oil affects marine life, watch this video from the Pew Environment Group that explains the impact of oil on marine life throughout the water column and check out this fact sheet from U.S. Fish and Wildlife which summarizes “Effects of Oil on Wildlife and Habitat.” (pdf) We may not know the full effects of the spill on animals - both big and small - for years to come. (See "Ecosystem Effects."

The Case for the Gulf

Dr. Sylvia Earle
Dr. Sylvia Earle (Select Committee on Energy Independence and Global Warming)

In testimony before a committee of the U.S. House of Representatives, Dr. Sylvia Earle, National Geographic Explorer-in-Residence and former chief scientist of NOAA, offered specific suggestions for addressing the catastrophic oil spill in the Gulf and delivered an impassioned call for greater investment in ocean research—including more expeditions to explore the Gulf’s deep waters, establishing permanent monitoring stations and protocols, and encouraging tri-national collaboration among scientists and institutions around the Gulf. “No one has descended to the greatest depth in the Gulf of Mexico, about three miles down in the Sigsbee Deep near Yucatan. In fact, no one knows for sure exactly where the deepest place in the Gulf is, or if they do, proving it has been an elusive goal,” she said.