Abstract: An electrode system for measuring oxygen gas in a solution comprises a pair of electrodes consisting of an indicator electrode and a reference electrode immersed in an electrolyte solution and a membrane pressed against the indicator electrode. On the other side of the membrane, is a solution to be analyzed. In determination of gas in solution especially in blood, good reproducibility of data, a stable reading and a long performance life are obtained by rubbing the surface of the indicator electrode and rotating a magnetic stirrer on the membrane. These effective measures prevent the electrode and the membrane from being contaminated. Accordingly, continuous analysis of arterial blood can be achieved.