This article reports the valence-band x-ray photoelectron spectroscopy (XPS) of various forms of sodium phosphate. Valence-band spectra are compared,to spectra generated from cluster and band-structure calculations. Five different forms of sodium phosphate are studied as follows, Na4P2O7, Na5P3O10, Na4P4O12, Na2H2P2O7, and NaH2P2O2. Core-level XPS studies are of little use for differentiating between such similar compounds while valence band photoemission has been found to be particularly effective at identifying subtle differences in surface chemistry. The results indicate that the valence-band region clearly distinguishes between these different phosphates and that these differences can be predicted by spectra generated from both cluster and band-structure calculations. (C) 2003 American Vacuum Society.