Abstract: A device for separating dissolved or entrained gas from a liquid and particularly for separating dissolved or entrained air from oil used in hydraulic systems or as electrical insulation. Contaminated oil, containing dissolved or entrained gas, is introduced into a degassing chamber where the gas is removed in a relatively low pressure atmosphere. The oil, with at least part of the gas removed is withdrawn from the chamber through a cycling valve which automatically closes when the oil in the chamber reaches a low level at the end of a degassing phase. After the cycling valve closes, the degassing chamber begins to fill with oil, and the rising oil level operates as a piston to expell the previously separated gas through a vent. When the oil completely fills the chamber, the vent closes and pressure within the chamber rises until a predetermined pressure is reached. The cycling valve then opens automatically, allowing the oil to again be withdrawn.