Ab initio electronic-structure calculations of surface catalysis often give changes >= 0.1 eV for activation energies of intermediate steps when the surface structure or composition is varied, yet >= 50-fold change in activity according to naive interpretation of the Arrhenius formula is usually not seen in corresponding experiments. To quantitatively analyze this sensitivity inconsistency between simulations and experiments, we propose a mean-field microkinetic model of electrochemical oxygen reduction reaction on Pt (111) and (100) surfaces, which outputs similar steady-state reaction rates despite of large differences in adsorption energies of reaction intermediates and activation energies. Sensitivity analyses indicate lateral repulsions between surface adsorbates ("enthalpic effect") and site competition ("entropic effect") flatten the catalytic activity vs. adsorption strength volcano plot and reduce sensitivity to material elementary energetics, in agreement with the observed experimental sensitivity behavior. Our analyses provide a systematic method to quantitatively investigate sensitivities of surface reactions when the mean-field approximation is reasonable. (C) 2012 Elsevier Inc. All rights reserved.