Impinging O-atoms react with adsorbed CO on Pt(111), Ir(111), and Ru(001), to form CO2 at surface temperatures as low as 77 K. The initial reaction probability is measured on these three surfaces using reflectivity techniques and is much lower on P(111) than previously supposed. The reaction probability is measured as a function of surface temperature, incident O-atom flux, kinetic energy, and angle. Interestingly, a significant dependence on incident angle is observed on all surfaces (the reaction probability is similar to 2.5 times greater at normal incidence than at glancing angles), and a kinetic energy effect is noted at the higher incident angles studied. Also, surface temperature is shown to have an effect on the reaction probability in measurements performed on Pt(lll) and Ir(lll) at normal incidence.