Using research results reported from oil spills, laboratory experiments and microcosm studies, this review outlines the many processes controlling the behavior of petroleum in marine waters. The fate of oil spilled at sea depends on the composition of the oil, and on such external factors as light and temperature. The extent of degradation depends on the type of coastal areas in which the spill occurs. In open, exposed areas, with good circulation of water, most oils are quickly degraded (Rashid, 1974). In protected shallow areas with poor-circulation spilled oil is incorporated into the fine sediment and much remains unaltered for many years (Blumer and Sass, 1972). Photochemical oxidation, dissolution, emulsification, adsorption to particles, biodegradation and uptake by zooplankton interact to affect the fate of oil slicks and oil in the water. Sedimentation deposits oil on the bottom where it can be resuspended into the water, penetrate deeper into the sediment or be degraded. The sediment community of microbes, meiofauna and macrofauna is responsible for the degradation of sediment oil.