A method of, and apparatus for, separating phases in a polyphase system is described and particularly in separating oil from produced water by the contact of gas bubbles and oil droplets by a dispersed gas flotation technique. A polyphase system is divided into at least two portions. The pressure of one portion is reduced to form bubbles of a gas, and the two portions are then recombined whereby the-bubbles in the mixture enhances flotation, and hence separation of the dispensed phase, e.g. oil, from the continuous phase, e.g. water. The invention has particular application in the oil industry and in other fields where efficient separation is required.