Abstract: A compact gravitational oil-water separator particularly adapted for use in small drainage systems in order to avoid pollution to the environment is provided with a plurality of separating components housed within a tank. More specifically, these components include a baffle member which provides initial separation of an incoming oil-water flow stream and distributes the flow substantially across the entire width of the tank. After the flow impinges the baffle member, the flow is directed downward towards a sediment bucket which captures any large particles separated from the flow and then the flow is directed upwardly at an angle through a coalescer unit. After exiting the coalescer unit, the flow is guided over a separation plate and then is re-directed, in a reverse direction, to an inlet opening of an outlet flow passage. By reversing the fluid flow, substantially the entire tank is utilized in the separation process.