This paper presents experiments and model predictions for the oxidation of CO over a platinum catalyst in a monolith reactor. Experimental behavior is broadly consistent with previously reported work on CO oxidation. Ignition–extinction (light-off) curves demonstrated the presence of multiple steady states with a hysteresis effect. The two branches corresponding to the two states of predominantly CO covered or oxygen covered. Admission of CO pulses to an oxygen covered surface results in reaction, indicating the occurrence of adsorption of CO on an oxygen covered surface. A model based on adsorption and surface reaction using the classical Langmuir–Hinshelwood (LH) approach qualitatively was able to reproduce the light-off behavior. The best model assumes dissociative chemisorption of oxygen on two surface sites. It was superior to a model proposing molecular adsorption of oxygen followed by rapid dissociation. Addition of steps allowing CO adsorption on an oxygen filled surface via an “oxygen compression” mechanism enable the qualitative description of the reactor response to step inputs of CO to an oxygen rich feed stream. Some parameter adjustment remains to allow a better fit between experiment and model predictions.