The total electric potential difference between a metal and a solution across an oxide film being built up by a constant anodic current is decomposed into three contributions: differences at the interphases metal‐oxide and oxide‐solution, both subject to activation overvoltage, and the difference across the oxide layer. For one or the other of the interphases the case of linearity of overvoltage with the logarithm of the current (in the range of large currents) and that of proportionality of overvoltage with current (in the range of small currents) are examined in some detail, and previously obtained experimental data for three types of titanium, for hafnium, and for tantalum are analyzed in terms of the proposed theoretical treatment. Numerical values are obtained for the various parameters appearing in the equations: thickness of the interphase, exchange current, electric potential difference, and electric field at zero current. Possibilities for refinement and extension of the treatment are mentioned.