Abstract: An apparatus for separating a relatively low density liquid such as oil from a relatively more dense liquid, e.g. water, substantially immiscible therewith, comprises a vessel in which the two liquids form strata, and a trough in the vessel is provided with a pair of floats. At least one of the floats is internally subdivided into at least a pair of laterally spaced trim chambers interconnected by a tube so that the introduction of compressed air into one chamber displaces trim liquid into the other and causes rotation of the float about an axis parallel to the trough so that the overlying liquid can flow over the edge of the trough into the latter when this edge is canted beneath the liquid surface.