x-ray photoelectron spectroscopy (xps) has been used to determine the surface composition of model p-aramid compounds and a number of poly(p-phenylene terephthalamide) fiber samples subjected to a variety of commercial and laboratory surface treatments. the surface compositions determined using xps are in accord with the thermodynamic results of a previous gas adsorption study of the same fibers using inverse gas chromatography (igc). in particular, the xps results show that a phase transition detected by igc in a removable surface layer on a number of fiber samples is associated with the presence of ester groups in the surface layer. both the negative entropy of adsorption, - $triangle open$ s//a**o, for alkanes, and the surface concentration of nitrogen are dependent upon the thickness of any surface layer on the fibers. an atomic surface concentration of 10.2 nitrogen was determined from near normal exit angle xp spectra of a laboratory-cleaned fiber sample, in close agreement with the expected value of 11.1. these results confirm the utility of both xps and igc in the study of fiber surface properties (author abstract) 23 refs