Abstract: A rotary engine has a first ring-shaped floor portion connected to an inner shaft for rotation therewith and a second ring-shaped floor portion connected to an outer shaft for rotation therewith. The annular floor portions cooperate with an engine casing to define an annular chamber. A first pair of diametrically aligned pistons are positioned within the annular chamber and are connected to the first ring-shaped floor portion while a second pair of diametrically aligned pistons are positioned within the angular chamber and connected to the second ring-shaped floor portion. The pistons cooperate to define a plurality of combustion chambers. Means are provided for causing combustion in the combustion chambers for imparting rotary motion to the inner and outer shafts.