A method for separating oil and water in a flow which comprises feeding the flow of oil and water (primary) mixture through an entry (182) into a vortex zone within (181) which, e.g., contains a helical coil shaped wall member (188) adapted to impart a rotational movement to the primary mixture so as to form a rotating fluid mass within which a non-turbulent vortex of oil (183) floats on secondary the mixture of water and the residue of the remaining oil. The secondary mixture is led downwards through an conduit (208) formed between the outer wall (195) of a chamber and an envelope (201) to the bottom of the lower housing where it encounters the bottom end of the first stacked group of tilted corrugated plates of the method. The plates withdraw oil from the secondary mixture. The recovered oil floats upwardly. It is guided by the barrier plates (193), (194) and the outer wall (195) respectively to the escape tube (198). This extends into the vortex zone and has an outlet 200 in or near to the floating oil vortex (183). The recovered oil passes through the outlet and mingles with the floating oil (183) and is carried away by pipe (186).
