Steady-state IR measurements for adsorption of only CO and under WGS reaction indicate that formates are present on the surface of partially reduced ceria, in contrast to a recent study, and that they are strongly limited at high CO conversions. At low temperatures and conversions, the formates are close to the equilibrium adsorption/desorption coverages obtained from CO adsorption alone. The formates are close to saturation at low temperatures. These IR results favor the bidentate formate mechanism in explaining WGS. However, more kinetic studies are required and over a wider range of temperatures. While low-temperature kinetic studies have found a zero-order dependency for CO and related this to saturation of a noble metal surface, this study indicates that one cannot rule out the possibility of the formate mechanism on this basis, as CO is also close to saturation as an adsorbed formate at the low temperatures used in previous studies.