Abstract: The invention relates to a separator for separating a mixture of two immiscible liquids of different densities, one of these being dispersed in the other. The separator which includes, superposed in a cylindrical tank, an injection chamber for injecting the mixture disposed between a coalescence chamber and a collecting chamber for collecting the dispersed component. The injection chamber (2) communicates with the coalescence chamber (3) via an annular passage (72) formed between the wall of the tank (1) and the periphery of a deflector (7) which separates said chambers and is also surmounted by funnels (70) which make the coalescence chamber communicate with the collecting chamber. The invention applies in particular to the treatment of bilge water on board ships or to the treatment of ballast water on board oil tankers.