New spectroscopic data on methanol oxidation at PtRu alloys are presented, showing the different behavior of 85:15 and 50:50 alloys towards the reaction pathway involving adsorbed CO. The higher activity for methanol oxidation, measured at the PtRu 85:15 as compared to the 50:50 alloy, is due to the contribution of parallel pathways reactions other products (i.e. HCOOH and/or HCHO). Methanol re-adsorption during the oxidation reaction is slower at the Ru richer alloy, however, for the pathway involving COad, methanol adsorption is not the rate-determining step. Analysis of IR spectra indicates that the latter is, more likely, the dissociation of water as the oxygen donor species. The activation energy of methanol oxidation reaction on both 85:15 and 50:50 alloy was found to be around 60 U mol(-1) as reported in the literature for other PtRu compositions. According to this high value of the activation energy, the experimental current is strongly dependent on the temperature and, consequently, when comparing the catalytic activity of the alloys towards methanol oxidation, the effect of small temperature differences should be taken into account. (C) 2003 Elsevier B.V. All rights reserved.