A pumping unit system having vertical sampson post, a walking beam pivotally supported at the upper end of the sampson post and a horsehead affixed at a forward end thereof that supports a reciprocated sucker rod string, including a gear reducer mounted at selectable positions on the walking beam and having a horizontally extending drive shaft, a crank arm affixed to the drive shaft the spacing between a selectable length pitman rod having a first end secured to said crank arm and a second end having a pitman bearing that is selectably mountable to a plurality of pitman bearing locations and a prime mover connected to the gear reducer and wherein the characteristics of the pumping unit are determined by the selectable position of the gear reducer, the selectable length of the crank arm, the selectable length of the pitman rod, and the selectable pitman bearing location.