An engine driven high-pressure micro-compressor has been developed which employs a unique driving principle. Its advantages make it ideal for supplying high-pressure gaseous fuel to direct injection gas engines. Possible arrangements of the compressor within the engine's fuel supply system are described. The ideal operating cycle of the compressor is described. A mathematical model based on the ideal thermodynamic cycles of the compressor and engine has been developed to predict its performance characteristics. The results presented show that this type of analysis gives an accurate prediction of the compressor cylinder pressure versus engine crank angle in comparison with experimental data.