Abstract: An internal combustion engine includes a pair of opposed piston assemblies that reciprocate within a single combustion chamber in an engine block. Each piston assembly includes an annular piston head that is received concentrically around a driveshaft which is rotatably driven by the piston assemblies. A supercharging chamber is concentrically disposed about each piston assembly. Pump rings connected to each piston assembly extend into the supercharging chambers and pump air through the chambers into an intake manifold as the piston assemblies reciprocate in each direction. Cooling lubricant is circulated through the engine block and piston assemblies as well as through and along the drive shaft so as to cool the combustion chamber on substantially all sides.