Abstract: A method and apparatus for pumping combustible gases at high pressure without raising the gas to its combustion temperature, the apparatus including a piston-type pump having an intake chamber communicating with a cylinder through intake valves, a discharge chamber communicating with the cylinder through discharge valves, the intake chamber and the discharge chamber having cooling means therearound for cooling gas in the chambers, the valving being such that gas must pass entirely through the intake chamber for maximum cooling on intake, and gas must pass entirely through the discharge chamber on discharge for maximum cooling on discharge, some gas being held in the discharge chamber during compression of the gas for maximum cooling.