Abstract: A membrane that is prepared in a water in oil system and comprises a hydrophobic polymer film having controlled porosity. Such membranes are particularly well suited for use in oil drilling processes; in the separation of oil from the waste water of oil refineries; in the separating of oil from the waste water resulting from cleaning oil tankers; and the separation of oil from water used in cleaning oil tanks or containers for industrial equipment. The membranes can also be used in the dewatering process of edible protein as well as the dewatering of liquid fragrances.