What Causes Oil Spills?

Sea-going, oil tanker-related spills dominate the popular imagination when it comes to oil spills. Oil can get out of a tanker in a variety of accidents. According to the International Tanker Owners Pollution Federation, the single largest cause of oil spills in tanker accidents is hull failure. This means that either due to a leak or storm damage, the structural integrity of a ship's hull fails. Six-hundred and seventy-one incidents of this kind took place between 1974 and 1999. ITOPF says that other major causes of tanker leaks are collisions, fires and groundings. Oil tanker accidents tend to be the most publicized and most harmful form of spill, because they have the potential to release a substantially larger amount of oil at once than any other spill.

A separate category of tanker accident is the spillage of oil resulting from a loading or unloading problem. Simply put, something causes oil to go overboard while it's being pumped into or out of a tanker. The ITOPF said that between 1974 and 1999, there were over 3,000 such incidents. That makes them the most frequent form of oil spillage involving sea-going tankers. However, almost all of these incidents were relatively minor compared to accidents like collisions and groundings, in which 93 percent of them involved a spill of 7 tons of oil or less.

A surprisingly major source of oil spills stem from the operation of motor vehicles. Minor, everyday spills and leaks of motor oil wind up poisoning the soil, or find their way down through storm drains into sewers, then into rivers, and eventually out to sea.

Oil is also spilled on land and at sea when it's extracted from underground reserves. After all, the popular (and sometimes still accurate) image of a newly tapped oil well is a literal geyser of oil spewing into the sky, and all that oil is spilled. Accidents in extracting oil from a well occur regularly, resulting in spillage.

Pipelines and tanks also leak oil, resulting in spills great and small. These leaks can be the result of natural catastrophes such as hurricanes and earthquakes, an accident like a collision, poor maintenance resulting in structural failure, or even deliberate vandalism or attack.

Oil is stored in underground reservoirs, and sometimes these reservoirs are disturbed by the movement of tectonic plates. This rarely happens on land, and when it does it's rarely a matter of concern. However, because oil is less dense than water, undersea tectonic disturbances can result in major oil spills.