The excess volume V-E, ultrasonic speed u and H-1 NMR measurements have been carried out in mixtures of hexamethylphosphortriamide (HMPA) and 2,2,2-trichloroethanol (TCE) or 2,2,2-trifluoroethanol (TFE) or 1,1,1,3,3,3-hexafluoropropan-2-ol (HFP) over the whole composition range. The excess volume and ultrasonic velocity have been measured with the help of continuous dilution dilatometer and ultrasonic time intervalometer based on a 'pulse-echo-overlap' (PET) technique, respectively at 303.15 K. V-E is positive throughout the whole composition range in the mixture of HMPA and TFE whereas it shows an S-shaped behaviour, negative at low x and positive at high x in the other two mixtures HMPA + TCE and HMPA + HFP. The V-E results have been utilised to calculate the partial molar volumes of the components. Estimates of the isentropic molar quantity K-S and of its excess counterpart K-S(E) were obtained from excess volume data in combination with ultrasonic speed values. The K E is positive for HMPA + TFE but negative for HMPA + HFP mixture. It is both negative and positive for HMPA + TCE with very small positive values at very high mole fraction of HMPA. The order is TFE > TCE > HFP. The apparent parameters have also been estimated for support in explaining the results of volume and compressibilities. An attempt has also been made to correlate these with the values of the spectral parameter Deltadelta (HMPA-halogenated alkanol) calculated from the H-1 NMR data.