Abstract: Apparatus for pumping fluid from a subterranean reservoir. The apparatus has in combination a well casing and a hollow tube disposed concentrically within the well casing. Secured to the end of the hollow tube is a hollow housing which includes a motor and a pump driven by the motor. An entrance conduit extends down the annulus between the tubing and the casing and carries a refrigerant working fluid which drives the motor in order to operate the pump which pumps subterranean fluids from the housing through the hollow tubing up to the surface of the earth. A return conduit extends from the hollow housing through the hollow tubing up to the surface of the earth. After the refrigerant working fluid expands and drives the motor, it is initially cooled. Subsequently, the refrigerant working fluid passes into the top of the hollow housing where it is vaporized within the return conduit as the return conduit is in contact with hot subterranean produced formation fluids.