Abstract: An internal combustion engine having a housing defining a pair of axially aligned and opposing cylinders with a lubricant chamber therebetween, a stationary piston in the housing extending through the lubricant chamber and having opposite ends disposed within the aligned cylinders, and a hollow cylindrical piston slidably received within the housing and around the stationary piston for reciprocal movement thereby forming a pair of first variable volume chambers between it and the aligned cylinders and a pair of second variable volume chambers between it and the stationary piston. A carburetor communicates with the second chambers through longitudinal passageways in the stationary piston so as to admit a charge of combustible fuel therein which is compressed and then injected into the first chambers for recompression and subsequent combustion, the compression and combustion cycles for the chambers on opposite ends being 180.degree. out of phase.