Abstract: A rotary fluid pressure engine having good fuel efficiency and low pollutant emissions. An annnular chamber of uniform cross-section forms a cylinder housing. An endless rotor is centrally positioned and movable in the cylinder housing. The rotor comprises at least one uniform thickness and height section which is connected to at least one enlarged height piston section, the rotor central width being approximately equal to the central width of the cylinder housing. At least one air floating valve member is formed in the cylinder housing, the valve members being movable by the enlarged height rotor section. The engine can be utilized to provide a compressed air source; to operate as a fluid pump; or utilized to turn a shaft.