The adsorption of CO2 on polycrystalline molybdenum is blocked even by the partial (aproximately two-thirds) presence of the strongly bound β2 oxygen. Pre-adsorption of CO2 at room temperature does not impede subsequent oxidation. The CO2 adsorption kinetics at room temperature can be explained by a two-site adsorption model with rapid dissociative chemisorption and carbon and oxygen in equivalent sites. On heating the CO2-saturated surface above 900 K, CO is lost from the surface. Interaction of CO2 at 1200 K gives a small buildup of carbon until the surface oxygen concentration increases sufficiently that the loss rate exceeds the deposition rate.