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Thermal excitation of adsorbed oxygen species is found to initiate the CO oxidation on Pt(111). We have prepared three different coadsorption systems to study the reactivity of different oxygen species; (1) CO on the O₂ preadsorbed Pt(111) surface, (2) CO on the nearly perfect Pt(111) p(2×2)‐O surface, and (3) CO on the disordered atomic oxygen‐preadsorbed Pt(111) surface. Four CO₂ desorption peaks (α‐CO₂ at 125 K, β₃‐CO₂ at ∼225 K, β₂‐CO₂ at ∼260 K, and β₁‐CO₂ at 320 K) are observed. The desorption temperatures of CO₂ strongly depend on the adsorbed states of oxygen species. We have shown that the α‐CO₂ state, β_2,3‐CO₂ states, and β₁‐CO₂ state are correlated with adsorbed O₂, disordered oxygen atoms, and p(2×2) oxygen atoms, respectively. The difference in CO₂ desorption temperature is related to thermal excitation of each oxygen species, which is derived from the structural …