High-resolution monochromated X-ray photoelectron spectroscopy (X.p.s.) (core line and valence band) was used to study polylethylene terephthalate (PET) as biaxially oriented crystalline film, spin cast amorphous film and amorphous polymer melt. On going from crystalline to amorphous PET the C 1s glycol component shifts similar to +0.10 to +0.14 eV, relative to the aromatic and carboxyl components. We ascribe this to the change from trans- to gauche-conformation of the glycol segment. Small differences occur in the valence bands of the crystalline and amorphous samples. Time-dependent studies demonstrate that the melt spectra are not significantly affected by thermal degradation. Under the conditions of the X.p.s. analysis molten PET behaves as an electrical conductor.