Abstract: A hybrid engine, having a plurality of coupled expansible chamber devices, preferably a piston in a cylinder, each capable of operating in any one of an internal combustion mode, an air pump/compressor mode and an air motor mode. The modes are controlled by a microcontroller which controls the valves, ignition source and fuel source. The mode for each expansible chamber device is computed and independently selected by the microcontroller and the combination of modes at any instant is switched to optimize engine operation for the operating conditions at that instant.