The passivation behavior of Cu-xZn (x = 10, 20, 30 and 40 wt. %) alloys and their individual metal components was studied in borate buffer, pH 9.2, by a combination of electrochemical measurements and X-ray photoelectron spectroscopy (XPS). In general, the shape of cyclic voltammograms of all four alloys resembles that of copper more than that of zinc metal. With increasing zinc content, however, several features originating from the zinc component appear. The composition of the passive film on electrochemically oxidized samples was determined by XPS spectra combined with X-ray induced Auger spectra. The passive film formed on Cu-10Zn alloy consists of Cu2O and CuO/Cu(OH)(2), together with a small amount of ZnO which cannot be detected electrochemically but only by XPS analysis. In the case of Cu-40Zn alloy the formation of ZnO is preferred in the passive film and substantially delays and reduces the formation of copper oxides. The ratio of Cu2O to ZnO, in addition to their thickness, was calculated as a function of potential by deconvolution of the Auger spectra. These values were in reasonable agreement with those deduced from electrochemical reduction curves. (C) 2003 The Electrochemical Society. All rights reserved.