A hydraulic oil well pumping installation includes a down hole pump positioned down a well, the down hole pump including a master cylinder and at least one slave cylinder in axial alignment with the master cylinder. A master piston is positioned in the master cylinder and divides the master cylinder into a first portion and a second portion. A slave piston is positioned in the at least one slave cylinder and divides the slave cylinder into a first portion and a second portion. The slave piston is connected by a rigid linkage to the master piston, such that movement of the master piston results in movement of the slave piston.