Abstract: The pump jack is of conventional API front-mounted geometry Class III configuration, but is provided with an angularly disposed walking beam, so as to be able to pump a slant rod string. To incorporate versatility into the unit so that a single model can be used with different wells having different angularities, there is provided: means for altering the effective length of the Pitman arms (so that the angularity of the walking beam is changed, which permits the unit to be used with a rod string having a different slant); means for bringing the counterweight into phase with the well load; and means for altering the stroke length.