Abstract: A method of and apparatus for re-processing waste oil for the production of a fuel oil substitute are described. The waste oil is passed first to a solids separation zone and then to a three phase separator in which the oil is intimately contacted with water. The plant is preferably operated continuously and the rate of supply of waste oil to the solids separation zone is controlled in dependence on the water content of the oil product from the three phase separator. A system of level controls and pressure switches is described which provide for automatic shut down of the plant in the event of "seal loss" in the separator or other malfunction of the plant.