Abstract: A method for treating waste cooking oil is disclosed, the method comprising subjecting the waste cooking oil to a first separation comprising a settling treatment at ambient temperatures to produce an oil fraction and a sludge fraction; and subjecting the oil fraction so recovered to a second separation comprising filtration. An apparatus for refining waste cooking oil comprises a settling system for separating the waste cooking oil into an oil fraction and a sludge fraction; a filtration system for filtering the oil fraction. The oil fraction recovered is particularly suitable for use as a fuel for an internal combustion engine and as a replacement for diesel in operating diesel engines.