Abstract: A gas-operated motor adapted to be driven by gas evaporated from a reservoir of liquefied carbon dioxide or the like. In order to overcome the problems generally associated with such motors due to the cooling of the gas as it evaporates from the liquid state in the reservoir and expands in the working chamber(s) of the motor, a chamber holding a substance which undergoes a change of state to release heat to the gas in operation of the motor is included. More particularly this chamber is located to be in heat conductive relationship both with the working chamber(s) of the motor and with a tortuous passage through which gas is supplied to the working chamber(s) and wherein superheating of the gas prior to its introduction to the working chamber(s) takes place.