Abstract: A hydraulically operated oil well pump jack utilizing a double acting hydraulically operated piston and cylinder assembly for pivoting the walking beam of an oil well pump jack, a linkage mechanism for operating a reversing valve to cause extension and retraction of the piston and cylinder assembly for oscillating the beam about a saddle bearing at the upper end of a stanchion or samson post together with a crossover cushioning device for controlling acceleration and deceleration of the oscillating walking beam to reduce abrupt tension forces exerted on the polish rod and sucker rods and also reduce impact forces on the oil well pump jack during oscillation of the walking beam.