A submersible pumping system for use downhole, wherein the system includes a pump, an inlet section for receiving fluid, a pump motor, and a viscometer. Pumping system operating parameters are adjusted based on wellbore fluid viscosity measured by the viscometer. The viscometer can be disposed deep in the wellbore, adjacent the pump, seal, motor, at the pump intake or anywhere on the pumping system. The viscometer may be connected to a control system for controlling the pumping system in response to viscosity measurement and may include a sonic viscometer. A method of operating a downhole submersible pumping system is included that measures fluid viscosity in the wellbore during production operations. Pumping parameters can be adjusted based on the measured viscosity.