The first stages of the anodic oxidation of Ag(111) and Ag(110) electrodes in NaOH solution were studied by potential sweep voltammetry and ellipsometry. It was found that in the potential region studied, dissolution of silver species and electrosorption of oxygen occur. The (110) face is much more reactive to oxygen than the (111) face. On Ag(ll0) oxygen is reversibly adsorbed via a process of random deposition. The half-width of the adsorption peak indicates attractive lateral interactions in the chemisorbed layer.