Densities, viscosities, refractive indices, and excess enthalpies have been measured at 308.15 K and at atmospheric pressure for poly(ethylene glycols) 200, 400, and 600 and poly(propylene glycols) 400, 725, and 2000 + diethyl carbonate over the whole composition range. Enthalpy values are all positive, while volumetric values are negative with the exception of the mixture containing poly(propylene glycol) 400, where an inversion of sign is observed. Viscosity deviations are negative for all mixtures. Viscosities and viscosity deviations display complex dependencies on the type of polymer and on its molecular mass. The experimental results were fitted to the Redlich-Kister polynomial. The results are qualitatively discussed in terms of molecular interactions.