The formation of cesium-gold alloys by the deposition of cesium on to a Au(100) surface has been investigated by both core-level (X-ray induced) and valence-level (He(II) radiation) spectroscopies. The stoichiometries of the alloy overlayer indicate the preferential segregation of cesium to the surface of the thinner films. Oxygen chemisorption generates three distinct oxygen species O2-(a), Odelta-(a), and O-2(delta-)(a) characterized by their O(1s) binding energies and is accompanied by dealloying. With increasing oxygen exposure, the peroxo species is the major one present at 298 K. Dealloying is temperature dependent and is not complete at 80 K. Two of the oxygen states, Odelta-(a) and O-2(delta-)(a), are reactive to carbon monoxide, forming carbonate species. Peroxo-type species are also formed readily by oxidation of pre-carbonated surfaces. The products formed from CO-O-2 mixtures depend on the mixture composition : with a 3:1 (CO:O-2) mixture at 298 K, O2-O2delta-, and and CO3 species are observed, while for very much richer CO-mixture (60:1) only O2- and CO3 species form; at 80 K both mixtures result in only peroxo (O-2(delta-)) and carbonate species.