The electrochemical oxidation of CO on metallic surfaces following a lattice-gas model, including effective lateral interactions between one of the adsorbates and species diffusion, is studied. The reaction occurs through a Langmuir–Hinshelwood (LH) mechanism in which adsorbed CO reacts with adsorbed hydroxyl species. The mean field approximation and dynamic Monte Carlo simulations have been compared. The effect of the molecular distribution and surface mobility of reacting species on the potential dependence of the CO oxidation rate is analyzed. The inclusion of lateral interactions into the reaction mechanism reconciles different experimental observations, such as island formation and fast CO diffusion. Results highlight the importance of effective interactions in the reaction kinetics and suggest that they should be taken into account when interpreting experimental data. Simulations are useful for an improved qualitative understanding of the kinetics of CO oxidation and other electrochemical LH reactions.