In this work we have measured liquid-liquid equilibria (LLE) and vapor-liquid equilibria (VLE) in aqueous solutions of poly(ethylene glycol) (PEG) and sodium sulfate. The liquid-liquid equilibria have been determined over a range of polymer molar masses (1550-6000 g/mol), pH values (5.2-8.1), and temperatures (293.15-313.15 K) using a density-sound analyzer. The VLE in the system water + PEG 3000 + sodium sulfate have been measured over the entire homogeneous mixing range at 293.15 and 313.15 K by vapor-pressure osmometry. To demonstrate that the experimental data do not contain any obvious thermodynamic inconsistency, we described VLE and LLE simultaneously using the osmotic virial equation (McMillan, W. G., Jr.; Mayer, J. E. J. Chem. Phys. 1945,13,276) extended with a Debye-Huckel term (Debye, P.; Huckel, E. Z. Phys. 1923, 24, 195, 305. Pitzer, K. S. J. Phys. Chem. 1973, 77, 268).