Surface-sensitive core-level photoelectron spectra excited by synchrotron radiation are presented for surface oxide phases of W in the monolayer range. Discrete chemically shifted core levels are observed and are shown to be associated with specific formal oxidation states by comparison with bulk reference compounds. Slight increases in the value of the core-level shift for each oxidation state as the surface oxygen content increases are attributed to changes in the screening response of the system. Decomposition of the spectra into the separate contributions from each oxidation state provides specific and quantitative chemical information about the surface oxides. This and similar studies should be particularly useful for characterizing the disordered systems typical in applied surface physics where clarity of interpretation is very important. © 1985, American Vacuum Society. All rights reserved.