Abstract: For the separation of a contaminated floating top layer of oil or oil substances, a continuous laminer flow is created on or near the surface, by placing a number of baffles (8, 8') in the path of the flowing liquid (V) as it moves through a tank (1). The total amount of liquid flowing through the tank (1) is now adjusted in such a way that the correct control of the upper laminar flow (5) and the dominant more turbulent lower flow near the bottom (9) of the tank (1) produces a controllable constant difference in height (delta h). This total difference in height (delta h) can also be attained by cascade operation.