Oil, like many natural substances, will biodegrade over a period of time into simple compounds such as carbon dioxide, water and biomass. Bioremediation is the term used to describe a range of processes, which can be used to accelerate natural biodegradation. More specifically biostimulation is the application of nutrients, and bioaugmentation or seeding is the addition of microbes specially selected to degrade oil.

Biodegradation occurs as a result of the oxidation of certain components of spilled oil by microbes such as bacteria, fungi, unicellular algae and protozoa. The rate at which this natural process occurs is limited by several factors including the temperature, and the levels of microbes, nutrients and oxygen present in the immediate environment. Other factors such as the chemical composition and the amount of weathering of the spilled oil are also important.

Although Bioremediation presents a good picture it is a very slow process and takes a long time to work fully. It can work effectively only on oil which is spread as a thin layer on water.

Bioremediation is not suitable for removing large amounts of oil and should only be considered where the concentration of oil is low as a final polishing technique.