A model for the anodic oxidation of metals in concentrated solutions is presented. It emphasizes the competitive processes of film formation and dissolution occurring at different sites on the electrode surface and features selective adsorption of anions from the electrolyte. These processes result in a second-order dynamic behaviour of the metalfilmelectrolyte system, producing a peculiar shape in the complex impedance plane. A kinetic scheme including two adsorbed intermediates and two dissolution paths was found to be able to reproduce semi-quantitatively the general features of the impedance spectra of copper, nickel, tin and antimony in concentrated H2SO4 solutions.