CO monolayer oxidation on glassy carbon supported 1-2 nm Pt nanoparticles is studied using potential sweep and potential step methods. The CO stripping peak on the nanoparticles is significantly shifted to positive potentials vs. the corresponding feature at bulk polycrystalline Pt. Current transients at nanoparticulate electrodes are highly asymmetric with a steep rise, maximum at theta(CO)approximate to 0.8-0.9, and a slow decay following t(-1/2). The experimental results are compared to the theoretical models of adsorbed CO oxidation described in the literature. A tentative model is suggested to account for the experimental observations, which comprises spatially confined formation of oxygen containing species at active sites, and slow diffusion of CO molecules to the active sites, where they are oxidized. The upper limit of the CO surface diffusion coefficient at Pt nanoparticles is estimated as approximately 4 x 10(-15) cm(2) s(-1). (C) 2003 Elsevier Science B.V. All rights reserved.