Vapour pressure measurements at high temperatures have been performed on plutonium oxide samples using a Knudsen cell coupled with a mass spectrometer. Different experimental conditions were applied for the derivation of the solid-gas phase relations for three composition in the Pu-O phase diagram: the (Pu2O3-PuO2-x) two-phase domain, the congruent vapourisation composition and near stoichiometric PuO2.00. The partial pressures of the gaseous species PuO2, PuO, and Pu were assessed from ionisation efficiency curves recorded at constant temperature. The vapour pressure results for different phase fields were discussed together with all the available literature data. (C) 2011 Elsevier Ltd. All rights reserved.