The O-2 adsorption on Ag(111) single crystal in the range of 300-500 K has been studied by XPS, ADXPS, and TPD. At room temperature, the O1s line observed at 530.0 eV goes down to 528.2 eV when the sample is heated to 420 K. The comparison of XPS and TPD data indicates that both lines can be assigned to chemisorbed atomic oxygen. The depth concentration profiles calculated on the basis of the angular-dependent XPS data show that the line at 530.0 eV is responsible for oxygen adsorbed at the surface, as opposed to that at 528.2 eV which is assigned to oxygen between the top and second silver layers. The formation of surface silver oxide is concluded in the latter case.