In this work we investigate the electrooxidation of glycerol on platinum nanoparticles in acidic media. By using in situ FTIR and isotopically labeled glycerol ((CH2OH)-C-13-(CHOH)-C-12-(CH2OH)-C-13) we follow the reaction during a full cycle of oxidation and unravel the role of some important species on the electrooxidation pathways. Results indicate that terminal (-(CH2OH)-C-13) and central (-(CHOH)-C-12-) groups are able to form adsorbed CO and that both contribute to the production of CO2, although the terminal groups are easier to be oxidized than the central one, probably due to the steric effect provoked by -(CH2OH)-C-13 which prevents the oxidation of -(CHOH)-C-12-. Moreover, glyceraldehyde seems to be an important intermediate for the generation of glyceric acid. (C) 2013 Elsevier Ltd. All rights reserved.