Why Do Oil Spills Happen? Causes, Examples, and Prevention

Oil spills seldom have a single cause.

The oil drilling platform Holly near Huntington Beach, California, with Catalina Island in background

Maureen Sullivan / Getty Images

Although oil leaks naturally from fractures in the earth, most oil spills are destructive and a result of human error. This includes equipment malfunction or breakdowns, lack of oversight, collisions, and deliberate acts of sabotage.

Here, we unpack all of the major reasons why oil spills have occurred throughout history, provide examples, and explore ways to prevent spills.

Equipment Malfunctions and Regulation

Accidents resulting in oil spills are most often the result of lack of sufficient regulation and equipment malfunctioning. The Exxon Valdez oil spill is one of the most infamous examples.

The Exxon Valdez Oil Spill

Teams of firefighters in protective gear cleaning the oil-blackened Alaskan coast following the Exxon Valdez oil spill.
Teams of firefighters in protective gear cleaning the oil-blackened Alaskan coast following the Exxon Valdez oil spill.

jean-Louis Atlan / Sygma via Getty Images

When the Exxon Valdez oil tanker ran aground on a reef in Alaska’s Prince William Sound in 1989, the captain, Joseph Hazelwood, was initially blamed. Reported to have been drinking that day, Hazelwood left the bridge as it traversed the Sound, leaving an unqualified third mate in charge. But the National Transportation Safety Board (NTSB) later concluded that multiple factors played a role, including a broken radar and fatigued, inexperienced crew members working under stressful conditions.

In addition, the NTSB found that the Exxon Shipping Company had failed to ensure proper supervision and adequate rest for the crew. There were also flaws in the U.S. Coast Guard’s vessel traffic system and the escort system meant to ensure safe passage.

The Santa Barbara Oil Spill

On January 28, 1969, workers on an offshore rig owned and operated by Union Oil had just drilled a new well nearly 3,500 feet beneath the seafloor. As they removed the pipe casing, a pressure difference led to a blowout that caused oil and gas to surge toward the surface. Workers attempted to cap the well, but this only intensified pressure. Natural fault lines cracked under the seafloor, releasing oil and gas for weeks.

While nominally caused by an equipment malfunction, the deeper cause was the oil company’s lack of preparation and federal oversight. Union Oil had neither a contingency plan nor adequate equipment and know-how to stop the spill. It later emerged that the federal government had issued Union Oil a waiver to sidestep safety measures that might have prevented the spill.

The BP Oil Spill

Pelicans recently cleaned of oil dry in an outside area at a wildlife rehabilitation center in Buras, Louisiana after the BP oil spill.
Pelicans recently cleaned of oil after the BP oil spill.

Spencer Platt / Getty Images

On April 20, 2010, the Deepwater Horizon oil rig, operated by BP, exploded in the Gulf of Mexico, killing 11 people. The explosion caused a leak in BP’s Macondo wellhead located nearly a mile below the water’s surface, releasing 134 million gallons of crude into the waters of the Gulf of Mexico over a period of months. 

An investigation by the Bureau of Ocean Energy Management and the U.S. Coast Guard found the primary cause of the explosion to be a faulty cement base of the 18,000-foot deep well. The investigation concluded that BP and the rig’s owner, Transocean Ltd., violated multiple regulations by cutting corners to reduce costs. 

Kolva River Spill

The 1983 Kolva River spill in Russia, when millions of gallons of oil infiltrated streams and fragile wetlands, pointed to the risks posed by poorly maintained pipelines. The problem persists. In the U.S. today, there are many aging petroleum pipelines vulnerable to leaks and spills.

Critics point to lax, infrequent inspections and inconsistent safety regulations and protocols as factors that increase the risk of pipeline spills. Pipelines suffer hundreds of leaks and ruptures every year.


Another key though less common cause of oil spills is destruction via ship collisions. There are several examples of oil tankers colliding with other ships, such as the 1972 Sea Star spill when a South Korean supertanker sank after striking a Brazilian tanker off the Oman coast, and the 1983 Nowruz Oil Field spill, when a tanker hit an oil platform in the Persian Gulf. 

Pipelines, too, can suffer breaches caused by collisions. One example is the recent spill just off the coast of Huntington Beach, California. While investigators continue the inquiry into its causes, they suspect the offshore pipeline was struck by a ship’s anchor.

Deliberate Acts

During the Gulf War, oil workers work to cap a well in a blowout, Kuwait, 1991. Other wells burn in the background.
During the Gulf War, oil workers work to cap a well in a blowout, Kuwait, 1991.

Allan Tannenbaum / Getty Images

The largest oil spill on record occurred during the Gulf War in 1991, when retreating Iraqis attempted to deter American forces by releasing oil directly into the Arabian Gulf. The 380 to 520 million gallon spill resulted in a 4-inch thick oil slick across 4,000 square miles.

Concerns have grown about oil rigs and infrastructure becoming targets of terrorism or other deliberate sabotage. Many oil spill response agencies have little experience with terrorism incidents, which require special preparations and security. Still, sabotage of oil pipelines and other infrastructure are common in some countries, including Colombia, where armed groups have routinely targeted them, leading to spills in the surrounding environment. Nigeria and Russia have seen similar rebel attacks on oil infrastructure. Often, resources are lacking to effectively respond to such attacks.

While big, dramatic spills grab headlines, millions of gallons of oil are illegally dumped at sea and on land every year. According to Marine Defenders, most human-caused oil spills in water come from intentional ship releases. The advocacy organization says more than 88 million gallons of oil is intentionally spilled into U.S. waters alone each year—nearly eight times more than the Exxon Valdez spill. The group works to change mariner attitudes and practices around illegal dumping. 

Preventing Future Spills

While extreme weather conditions and natural disasters lead to accidents involving drilling and transportation systems, humans are ultimately responsible for the majority of oil spills. 

There are many opportunities for improvement by enacting more stringent standards, protocols, and regulations. But while these reforms have the potential to significantly reduce oil spills and their impacts, they will not prevent all spills.