Steady-State multiplicity of the N2O + CO reaction over an alumina supported platinum catalyst has been observed over the temperature range 461-520 K. The boundaries of the steady-state multiplicity region have been mapped on a N2O-CO feed composition diagram, and the effect of temperature on multiplicity was determined. Four kinetic models have been examined, and it was found that only a model based on carbon monoxide self-exclusion from the platinum catalyst was able to describe all of the observed behavior. The CO self-exclusion effect requires that an adsorbed CO molecule exclude other CO molecules from an area equivalent in size to N(CO) surface Pt atoms, where N(CO) is slightly greater than unity. The proposed mechanism consists of several elementary steps, namely, the reversible adsorption of CO, the irreversible dissociative adsorption of N2O to form adsorbed atomic oxygen and gaseous N2, and the reaction of adsorbed carbon monoxide and atomic oxygen to form gaseous CO2. Due to the CO self-exclusion effect, N2O can still adsorb on a Pt surface saturated with CO and therefore the model predicts CO conversions as high as the experimental values for high concentrations of CO in the feed, something which is not possible with the other three mechanisms which were examined. For this model, the steady-state multiplicity can be described by an explicit rate function.