Dielectric measurements were obtained on poly(propylene glycol) (molecular weight: 4000 Da) at pressures in excess of 1.2 GPa. The segmental (a process) and normal-mode W process) relaxations exhibited different pressure sensitivities of their relaxation strengths, as well as their relaxation times. Such results are contrary to previous reports, and (at least for the dielectric strength) can be ascribed to the capacity for intermolecular hydrogen-bond formation in this material. With equation-of-state measurements, the relative contributions of volume and thermal energy to the a-relaxation times were quantified. Similar to other H-bonded liquids, temperature is the more dominant control variable, although the effect of volume is not negligible. (C) 2003 Wiley Periodicals, Inc.