Abstract: Methods and apparatus for filling containers with a gas or gas mixture under pressure are disclosed. The apparatus comprises a fixed volume vessel for containing the gas at a pressure P.sub.1, a line extending from the fixed volume vessel to a buffer volume vessel which has a capacity greater than the volume of the container to be filled, a pressure controller for controlling the pressure of the gas in the line so that the gas reaches the buffer volume vessel at a pressure P.sub.2 which is less than P.sub.1, a further line extending from the buffer volume vessel to at least one filling nozzle, and a valve located in the further line for controlling the flow of gas from the buffer volume vessel to the gas capsule to be filled.