The surface potential of Y2O3 stabilized ZrO2 was measured at 1035 K during the re-equilibration involving oxidation and reduction at oxygen partial pressure between 0.21 and 3.10-4 atm. Changes in work function consist of a rapid initial increase due to ionic equilibration and a slow drift of the same sign. Comparison of the obtained results with former electronic emission data of ZrO2 reported by Odier and Loup enables to determine the exponent of oxygen partial pressure dependence of Pt covered with a thin layer of PtO2 /n = 8.1/