A pressure actuated, rodless pump for pumping fluid preferably from a well through a tubing string comprises a chamber and a check valved movable piston which define a pump cavity, the chamber having a check valved outlet to the tubing string on the cavity side of the piston and a fluid inlet on the other side of the piston. The piston is connected to a spring assembly by a pull rod. The spring assembly includes a cylinder having an elastomeric bladder separating a gas filled chamber from an upper fluid chamber which is separated from a lower fluid chamber by a wall having a fluid passageway formed therein. The lower fluid chamber encloses a stationary piston and both the lower and upper fluid chambers are in fluid communication with the tubing string through a charge valve. Cyclic pressure applied to the fluid in the tubing string forces the cylinder and movable piston downwardly to draw fluid into the pump cavity and to force fluid from the lower fluid chamber into the upper fluid chamber to compress the gas. Alternating with the cyclic pressure, the compressed gas expands forcing fluid from the upper to the lower fluid cavity to move the cylinder and the movable piston upwardly and release fluid from the pump cavity to the tubing. The charged valve functions during the pressure cycles to replace fluid lost from the lower fluid chamber past the stationary piston.