Abstract: A pump unit for recovery of hydrocarbon liquid from atop water in a well includes a hydrocarbon pump intake with a linear probe for indicating the position of the pump intake relative to the hydrocarbon/water interface on a control panel, so that its relative position can be monitored and changed. The probe has a conductive member coated with a non-conductive coating, and is attached to a source of low frequency electrical signal. The strength of a signal output from the probe indicates the position of the probe, and the pump intake, relative to the hydrocarbon/water interface and controls a display on a control panel. Furthermore, the signal can be used to control the hydrocarbon/water interface relative to the pump intake by such means as pumped water from under the pump intake in a controlled manner to change said interface relative to the intake or by means of a motorized lift to reposition said pump intake relative to the interface.