Abstract: A method is provided for measuring the amount of gas in a liquid system which comprises a tank and a vacuum pump. The method includes the steps of operating a vacuum pump to exert a predetermined vacuum upon the liquid in order to desolubilize gas from the liquid and then separating the desolubilized gas from the liquid. The flow rate of the separated gas is measured by a flow meter and the amount of gas remaining in the liquid is determined as a function of this measurement and displayed by the flow meter. Gas measurement apparatus is provided for use with a liquid system and comprises a tank, a vacuum pump and a flow meter. This apparatus can be used in combination with an auxiliary hydraulic circuit adapted for use as part of a test bench for performing tests on a primary hydraulic circuit.