Abstract: An internal combustion engine of the rotary type which includes a cylindrical rotor having a skirt portion, rotating in an annular chamber, that comprises two arcuate walls of differing radii joined by relatively short, diametrically disposed sloping portions that serve as pistons. A sliding divider which extends through the annular chamber and the skirt portion establishes, with the sloping skirt portions, sub-chambers in the annular chamber in which compression of a combustible gas mixture and combustion of the mixture take place, the latter producing power for moving the rotor and the power shaft attached thereto. The divider is provided with longitudinallly spaced slots in which the rotor skirt is engaged whereby the divider is reciprocated as the sloping portions of the skirt pass through the slots.