A method and apparatus for controlling the operation of a steam turbine system, which system includes a source of steam under a controllable pressure, a plurality of governor valves connected between the source and the turbine first stage, each governor valve being movable between two selected positions each creating minimum steam flow throttling losses, a system control device (2) for producing a system control signal representative of the desired power level to be supplied by the turbine system, and a governor valve control (8) connected for producing a valve control signal in response to an input signal and for positioning each governor valve in accordance with the value of the valve control signal. During operation, the input signal to the governor valve control (8) is given a value which is based on the system control signal and which causes the valve control signal to have a value which will place each governor valve at least approximately at a selected position. In order to position the governor valves more accurately, the rate of flow of steam from the steam source is measured (18); the difference between the measured rate of flow and the expected rate of flow of steam from the steam source is determined (20, 24); and the value of the input signal to the governor valve control is modified (6, 12) in response to the difference determined in a direction to vary the positions of the governor valves in a manner to reduce the magnitude of that difference.