The steady-state catalytic oxidation process of carbon monoxide on platinum metal surfaces is studied using two irreversible kinetic computer simulation models: (a) An extended version of the model introduced by Ziff, Gulari, and Barshad (ZGB) with the effects of CO desorption and diffusion as well as finite reaction probability taken into account. The different physical processes, diffusion and desorption are studied independently and their effect on the equilibrium window, i.e., the regime where steady CO2 formation occurs is determined, (b) An interaction model where adatom-adatom nearest-neighbor (nn) interactions are taken explicitly into account through Boltzmann terms J1, J2, and J3 which are the energies of the CO-CO, O-O, and CO-O interactions, respectively. The phase diagrams in the temperature-CO-partial pressure ( T,pco-) plane are determined for different values of the nn interactions. The behavior of the system is dependent on the sign of J1 ( = J2 in the simulations) as well as the sign of the difference J1 -J3. There is thus a clear analogy with a two-component equilibrium lattice gas with nn interactions.