Various Cs oxides formed on the Ag(lll) and Ag(110) single crystals depending on cesium coverage, oxygen pressure have been identified by XPS and TPD. The comparison of the determined characteristics with the data for the Ag/Al2O3 catalysts allows us to select those of the Cs-O structures which are common for both types of samples: cesium peroxide and cesium suboxide. Mechanisms of their influence onto routes of ethylene oxidation are discussed.