We use cyclic voltarnmetry (CV) on fuel cell electrodes to elucidate the important differences between adsorbates resulting from carbon monoxide adsorption and methanol adsorption onto commercial Pt/C electrocatalysts in a sulfuric acid electrolyte. Under open circuit conditions, methanol was found to adsorb preferentially onto the Pt sites associated with "strongly bound" hydrogen. The sites associated with "weakly bound" hydrogen adsorbed methanol more slowly. In the case of CO adsorption, which requires no adsorbate dehydrogenation, all adsorption sites showed similar affinity towards the adsorbate. Electrochemical oxidation of the adsorbates derived from both methanol and CO exposure exhibit slower oxidation when the adsorbate is associated with cubic-packed-like sites than from close-packed-steps and other sites. NMR of a (CO)-C-13-adlayer prepared by electrochemical adsorption from low concentration (CH3OH)-C-13 shows a lower NMR shift and smaller linewidth than the previously reported values for electrochemically adsorbed (CO)-C-13 gas. These results are interpreted in terms of adsorbate motion on the electrocatalyst surface. (c) 2007 Published by Elsevier Ltd.