Abstract: A method and apparatus for Varying the speed of operations of an oil well pumping unit powered by a motor wherein variations in oil viscosity may be efficiently accommodated. An oil well pumping unit which includes a submersible pump actuated by means of a reciprocating string of sucker rods is monitored for both rod position and load present on the sucker rods. The oil well pumping unit is driven by an electric or gas motor through a controllable coupling and the speed of the oil well pumping unit is then varied, utilizing the controllable coupling, in response to variations in sucker rod load. As the lowering of the sucker rod is impeded by high viscosity oil, the load on the sucker rod decreases. This decrease in sucker rod load is utilized to decrease the speed of the oil well pumping unit by means of the controllable coupling to ensure that bridle separation does not occur.