A vacuum pumping system comprises a first gas supply for supplying a first gas, such as xenon, to a vacuum chamber. A pump receives the gas output from the chamber. A second gas supply supplies a purge gas, such as nitrogen or helium, for pumping with the first gas. A gas separator receives the pumped gases exhausted by the pump, and recovers the first gas and the purge gas from the stream. The recovered first gas is recirculated through the vacuum chamber, and the recovered second gas is recirculated through at least the pump.