Waste Vegetable Oil (WVO) is vegetable oil that has become unfit for food preparation due to chemical degradation (oxidation, hydrogenation) and/or accumulation of contaminants.

Historically, it has been used mainly as an animal feed additive or burned in waste-to-energy plants. As of 2003, the use of waste vegetable oil in animal feed is no longer permitted in the European Union, but continues in the United States.

Since the early 1990s, the use of waste vegetable oil to produce biodiesel has been growing steadily.

WVO may be used as waste SVO (after hot-water-wash) in diesel engines and to produce soap too.

As of 2000, the United States were producing in excess of 11 billion liters of waste vegetable oil annually, mainly from industrial deep fryers in potato processing plants and snack food factories and from fast food restaurants.

Waste vegetable oil has a stable market value of approximately USD 0.40 per gallon as of 2003, enough to make collection economically viable.