A separator for separating a relatively small volume e.g. up to 20% of a less dense liquid from a larger volume of a more dense liquid, for example for separating small volumes of crude oil from produced water from an oil-well, in the form of an elongated tube of reducing cross-sectional area. The separator has at least one tangentially-disposed inlet (5,105) for the mixture of liquids, adjacent the wide end of the separator, an outlet (10, 121) for the more dense compartment at the narrow end, and an axially disposed outlet (11,122) for the less dense component. A further outlet (6, 113) for the more dense component may be provided intermediate the two ends. The two outlets (10, 121 or 6, 113) for the more dense component are provided with pressure control means (85, 93) for controlling the pressure of the more dense component.