Abstract: A rotary motor/pump operating from pressurized elastic fluids (steam, and gases of all types), and a pump for either elastic or incompressible liquid fluids. With a combustion chamber (52) installed, motor (20) will also operate as a gas engine. The motor (20) comprises a casing (22) surrounding at least one pair of rotors (30) mounted on parallel shafts (28). The motor (20) is provided with inlet port (24) which admits high pressure steam or gas. Pressure is confined and applied continously and simultaneously to two outwardly extending lobes (34) which instantly apply torque to shafts (28). Cooperating cavities (40) permit lobes (34) to pass through the adjacent rotor (30) and maintain a seal during the passage. Timing gears (32) are attached to shafts (28) and maintain synchronization between lobes (34) and cavities (40).