We report here on a combined experimental and computational investigation of oxygen interaction with Ag(511), a vicinal surface of Ag(100) characterized by a high density of close-packed steps. The different adsorbed species, either molecular or dissociated, and their reactivity towards CO are characterized by vibrational and photoemission spectroscopy, while the possible adsorption sites are determined by density functional theory calculations. The initial phases of Ag 2 O nucleation are also observed; the role of step geometry in the oxide formation process is discussed in comparison with previous results for Ag(210).