More than 5 years after BP Deepwater Horizon, effects of oil spill linger

The BP Deepwater Horizon offshore drilling rig made history. In September 2009, it drilled the world’s deepest oil well, over six miles deep, in the Gulf of Mexico. Built in 2001, Deepwater Horizon was an ultra-deepwater semi-submersible drilling rig leased to BP Petroleum from 2001 through the fall of 2013. It was built for Transocean, the largest offshore drilling contractor, and it worked with a Transocean crew.

In February 2010, it began exploratory drilling in the Gulf’s Mississippi Canyon in water 5,000 feet deep. The rig had finished cementing steel casing at depths over 18,000 feet.

In the final drilling stages, a geyser of seawater erupted onto the rig, followed by a mix of mud, methane gas, and water. An attempt was made to activate the blowout preventer, which failed, as did the blind shear arm, a component of the blowout preventer designed to seal off the well in case of a blowout. The gas ignited into a series of explosions, then a firestorm.

The rig blew up on April 20, 2010, killing 11 of the 126-member crew and creating an environmental disaster of historic proportion.  The oil spill continued until July 15, 2010, when it was capped. It was declared officially dead on September 19, 2010.

The spill was the worst US environmental disaster.


  • This accident spilled 4.9 million barrels of crude oil. The oil is still not gone. While most oil evaporated, dissolved, or dispersed, studies in 2014 and 2015 found that up to 10 million gallons remain on the ocean floor.   
  • The oil spill contaminated more than 1,100 miles of Gulf coastline, at least 1,200 square miles of the deep ocean floor, and 68,000 square miles of surface water.
  • At risk were eight US national parks, over 400 marine species that live in Gulf islands and marine lands, and migratory birds.   
  • Estimates of lost tourism dollars were projected to cost the Gulf coastal economy up to $22.7 billion through 2013.
  • The incident brought out 48,200 responders, including 7,000 Coast Guard personnel.
  • A 2011 study using NASA and NOAA data showed that toxic compounds from the spill became airborne and significant amounts came onshore as rain, explaining why people on the Gulf Coast reported raining oil and dispersants.  

Marine Life

  • Commercial fishing in the Gulf is estimated to have lost $247 million as a result of fisheries that closed following the spill.
  • Traces of oil in the zooplankton show the oil compounds may be working their way up the food chain. They are eaten by baby fish and shrimp.  The plankton foraminifera died wherever there was an oil plume, further putting the Gulf’s food chain at risk.
  • A federally funded study from early 2014 found that low concentrations of crude oil may impact developing fish hearts and cause irregular heartbeats, cardiac arrest, and effect swimming ability in Atlantic bluefin tuna, which spawn in the Gulf. Other large fish, like swordfish, were also affected.
  • A 2014 government report on bottlenose dolphins in an area of Louisiana that experienced heavy and prolonged oil exposure found that 65 percent were seriously ill, dying, or not expected to live. These conditions were significantly worse than with dolphins studied in area unaffected by oil in Florida.  The longest and largest die-off of Gulf dolphins occurred, but deaths recently began to decline.


  • Nearly 1 million coastal and offshore seabirds are estimated to have died as a result of the oil spill.
  • Two years after the spill, 90 percent of pelican eggs contained petroleum compounds and 80 percent contained an agent used in cleaning the spill. Pelicans nest in the Gulf of Mexico. These agents can cause developmental abnormalities and reproductive problems.

Economic Costs

  • BP agreed to pay $2.4 billion and Transocean agreed to pay $1.4 billion for violations to the US Clean Water Act in 2013.  
  • In July 2015, an agreement was announced in which BP would pay $18.7 billion for Clean Water penalties, natural resource damage claims, and economic claims. It includes:
    • A civil penalty of $5.5 billion under the Clean Water Act, paid to the US.  
    • $7.1 billion to the US and the five Gulf states for natural resource damages, in addition to the $1 billion already committed for early restoration.
    • $232 million will be set aside to be added to the restoration interest payment to cover any further natural resource damages that are not yet known.
    • $4.9 billion over 18 years to settle economic and other claims made by the five Gulf Coast states.
    • Up to $1 billion to resolve claims made by over 400 local government entities.
  • BP also set up a fund of $2.3 billion for the seafood industry, of which $1 billion had been paid out as of December 2013.
  • Halliburton set up a $1.1 billion settlement fund to compensate businesses and property owners affected by the spill.
  • In 2010, BP agreed to pay Florida $25 million to promote its coastline, and $15 million more each to Alabama, Louisiana and Mississippi.

Environmental Threats from Oil Wells in the Gulf of Mexico

  • In the past 60 years, 50,000 wells have been drilled in the Gulf. Of these, 23,500 have been permanently abandoned and 3,500 were temporarily abandoned.  
  • An additional 3,200 oil and gas wells classified as active lie abandoned, with no cement plugging to help prevent leaks, posing an even greater risk to the environment.
  • The unused but officially active wells means at least 60 percent of the 50,000 wells ever drilled in the Gulf have been left with no routine monitoring for leaks. The metal and cement lining inside abandoned wells, as well as the plugs can break down over time and leak. Petroleum or corrosive brine, which is saltier than seawater, can leak from under the sea floor and harm sea life.
  • After the Deepwater Horizon accident, the Obama administration required oil and gas companies operating in the Gulf to plug the 3,500 temporarily abandoned wells and dismantle about 650 production platforms that are no longer used. However, it involves using the same inadequate sealing technology.

Additional resources

Deepwater Horizon Reading Room:

Deepwater Horizon Joint Investigation Team Releases Final Report:

Offshore Oil and Deepwater Horizon Social Effects on Gulf Coast Communities: