Recent experimental studies of the hydrogen oxidation reaction (hor) on platinum microelectrodes have shown the existence of a shoulder in the steady state polarization curves. An explanation for this behavior is presented on the basis of a rigorous kinetic treatment involving the Tafel-Heyrovsky-Volmer (T-H-V) mechanism. It has been found that such behavior is due to the significant variation of the reaction rates of the Tafel-Volmer (T-V) and Heyrovsky-Volmer (H-V) routes with overpotential (eta). At low eta values, the T-V route dominates the kinetics of the hor, reaching values close to the maximum rate corresponding to this route. At higher eta values, the contribution of the H-V route increases while that of the T-V route diminishes. On this basis, the experimental results were accurately correlated and the corresponding elementary kinetic parameters were evaluated. The contribution of the different types of microelectrodes to the improvement of the determination of the kinetic parameters for the hor is also discussed. (c) 2006 Elsevier B.V. All rights reserved.