The liquid-liquid equilibrium for the ternary systems PEG1000 + MgSO4 + H2O, PEG3350 + MgSO4 + H2O and PEG8000 + MgSO4 + H2O has been obtained experimentally. The results are fitted to a three-parameter equation which fits the results to within +/- 2%. Tie lines have also been measured, along with the viscosity and density in both phases. The tie-line compositions have been fitted to Bancroft’s potential equation.