A high-pressure gas compressor comprises a single-acting cam driven piston with a pressure compensation chamber disposed between the piston and the cam. A roller tappet assembly transmits reciprocating motion from the cam to the piston. A pressurized gas directed to the pressure compensation chamber offsets forces acting on the piston from the compression chamber gas pressure, thereby reducing Hertzian pressure between the tappet roller and the cam. Overall efficiency and durability can be improved by reducing friction between compressor components, for example by employing thin film coatings to reduce friction, pressurized oil lubrication systems and higher cylinder bore diameter to piston stroke ratios. The service life of gas seals and compression efficiency can be improved by thermal management strategies, including liquid-cooled compressor cylinder liners and intercoolers between compression stages. Employing a poppet-style intake valve and reducing parasitic volume in the compression chamber can improve compressor volumetric efficiency.