In order to derive the potential distribution in anodic films formed on zirconium in 1 M H3PO4, various optical and electrochemical techniques have been employed. All of the results demonstrate the existence of a linear relationship between the film thickness and the applied voltage. Once the films are formed, neither chemical nor electrochemical dissolution of the metal oxide can be observed in our electrolyte. The applied potential proves to be distributed over a space charge region, presumably located at the metal/film interface, and the neutral oxide, as can be concluded from capacitance-voltage (cv) profiles. A band model is proposed in which the energies of the conduction and valence bands are compared with the work function of Zr. Also the space charge region at the metal/film interface is included. This model not only fully accounts for the cv profiles, but also explains the observed strongly rectifying current-voltage (i-V) behavior, in the cathodic and anodic regions.