The oxidative ethanol adsorption and electrochemical surface reactions of adsorbed intermediates were studied on electrodeposited Pt, Ru, Pt0.92Ru0.08 and Pt0.85Ru0.15 in 1 M HClO4. A flow cell procedure was performed in order to separate surface reactions of intermediates formed in the oxidative ethanol adsorption from those reactions for ethanol in the bulk electrolyte solution. Oxidation and reduction reactions of adsorbed species were studied by potential-controlled electrodesorption spectrometry. No adsorbate formation was observed on a pure Ru electrode. In all cases, CO2 was the sole product formed in the oxidative electrodesorption of the adsorbates. Using (CH3CH2OH)-C-12-C-12 and (CH3CH2OH)-C-12-C-12, the oxidation reaction pathways of each C-atom to CO2 were followed. On the other hand, methane and ethane were detected during the reductive electrodesorption of adlayer species. The onset potential for these reduction products shifts to more negative potentials as the Ru content of the alloy increases. The methane to ethane yield ratio decreases in the sequence Pt > Pt0.92Ru0.08 > Pt0.85Ru0.15. A critical interpretation of the experimental data leads to a tentative yield of different adsorbed species as function of the Ru surface concentration.