A novel mode of operation of an oxygen pump-gauge device providing a linear and almost continuous output is described. The principle of operation is based upon the operation of the device in a feedback loop in which current is applied to the pump so as to maintain a sinusoidal gauge EMF of constant amplitude and frequency; theory predicts the amplitude of the ac pumping current required to be proportional to the oxygen partial pressure in the sample ps. Experimental results showed excellent agreement with theory.