Methods and systems are described for determining a flow rate of a gas-liquid fluid mixture in a conduit. In the described systems and methods, the fluid mixture is conditioned so that the liquid in the mixture is separated from the gas in the mixture. Properties of the conditioned flow may then be measured to determine the flow rate. In an embodiment of the invention, the hold up of the separated liquid is measured; the velocity of the separated liquid is measured; the velocity of the separated gas is measured; and the flow rate of the gas-liquid fluid mixture is determined from the hold up and the velocities.