Abstract: Two dissolved gas components in sample water, for example, oxygen and hydrogen in core water, are readily quantitatively determined in one and same membrane-type oxygen meter by using a membrane producing an overlapped potential region where a potential region for an oxidation limiting current plateau is overlapped with that for a reduction limiting current plateau between two dissolved gas components, and applying to between a pair of an electrode and a counter-electrode a more positive potential than the equilibrium potential for oxidation-reduction reaction of one of the two dissolved gas components principally, thereby measuring a current generated between the electrodes, and a more negative potential than the equilibrium potential for oxidation-reduction reaction of the other dissolved gas component, when desired, thereby measuring a current generated between the electrodes, and quantitatively determining a concentration of the first dissolved gas component from the latter current quantity and quantitati