Oil is also released into the environment from natural geologic seeps on the sea floor. Most human-made oil pollution comes from land-based activity, but public attention and regulation has tended to focus most sharply on seagoing oil tankers.

Environmental effects

Marine mammals exposed to oil spills are affected in similar ways as seabirds. Oil coats the fur of Sea otters and seals, reducing its insulation abilities and leading to body temperature fluctuations and hypothermia. Ingestion of the oil causes dehydration and impaired digestion.

Largest oil spills

Estimating the volume of a spill

By observing the thickness of the film of oil and its appearance on the surface of the water, it is possible to estimate the quantity of oil spilled. If the surface area of the spill is also known, the total volume of the oil can be calculated.

Oil spill model systems are used by industry and government to assist in planning and emergency decision making. Of critical importance for the skill of the oil spill model prediction is the adequate description of the wind and current fields. There is a worldwide oil spill modelling (WOSM) program.

Methods of cleaning

Methods for cleaning up include:

• Bioremediation: use of microorganismshttp://www.enviroliteracy.org/article.php/540.html or biological agents to break down or remove oil
• Controlled burning can effectively reduce the amount of oil in water, if done properly. But it can only be done in low windFact: date=December 2007, and can cause air pollution.
• Dispersants act as detergents, clustering around oil globules and allowing them to be carried away in the water. This improves the surface aesthetically, and mobilizes the oil. Smaller oil droplets, scattered by currents, may cause less harm and may degrade more easily. But the dispersed oil droplets infiltrate into deeper water and can lethally contaminate coral. Recent research indicates that some dispersants are toxic to corals.Barry, Carolyn (2007). Slick Death: Oil-spill treatment kills coral, Science News vol. 172, p. 67.
• Watch and wait: in some cases, nautural attentuation of oil may be most appropriate, due to the invasive nature of facilitated methods of remediation, particularly in ecologically sensitive areas. Fact: date=December 2007
• Dredging: for oils dispersed with detergents and other oils denser than water.
• Skimming: Requires calm waters
• Solidifying Fact: date=June 2007