We have measured the equation of state surface over the whole composition range for the mixtures poly(propylene glycol) + ethanol and poly(propylene glycol) + n-hexane up to 40 MPa. The excess volume for the system with ethanol is negative, decreasing in magnitude with increasing pressure. For the system with n-hexane, the excess volume becomes positive at high pressure and presents a complex shape with two changes in curvature along the composition axis. The p-rho-T data obey a superposition principle that makes it possible to build a master curve once the p-rho-T surface is known at a given pressure. The master curve depends on a single system-dependent parameter. The results have been analyzed with a lattice fluid model. The inclusion of hydrogen bond contributions in the model does not improve the prediction of the p-rho-T data for the system with n-hexane, while it makes a significant contribution in the system with ethanol, especially in ethanol-rich mixtures.