The electrooxidation of CO on polycrystalline Pt in 1 M HClO4 at 23°C under potentiodynamic conditions exhibits a double current peak. Whether a single or a double current peak is formed depends to a great extent on the amount of CO surface coverage. The present report attempts to explain the behaviour of the electrochemical reaction in terms of a single model involving the participation of two CO adsorbed states on polycrystalline Pt.