oil spill is a release of a liquid petroleum hydrocarbon into the environment due to human activity, and is a form of pollution. The term often refers to marine (Marine (ocean)) oil spills, where oil is released into the ocean or coastal waters. Oil spills include releases of crude oil from tankers (Oil tanker), offshore platforms (Oil platform), drilling rigs and wells (Oil well), as well as spills of refined petroleum products (such as gasoline, diesel (diesel fuel)) and their by-products, and heavier fuels used by large ships such as bunker fuel, or the spill of any oily refuse or waste oil. Spills may take months or even years to clean up.

Oil also enters the marine environment from natural oil seeps. 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.