PEG (4000 or 8000)-(Ammonium or Sodium) Sulfate Aqueous Two-Phase Systems were characterized at 278.15, 293.15 and 308.15 K. Two physical properties (density and refractive index) were used to obtain the compositions of the ends of the tie-lines. The binodal curve was constructed from these end points. A comparison with some available data at close temperatures allowed for assessing different experimental techniques. Data correlation for the experimental binodal curves and tie-lines was carried out using Merchuk and Guan's equations. The effect of temperature, polymer molecular weight and nature of the cation of the salt on the phase diagram were assessed using these models. It has been found that the heterogeneous region increases with temperature, polymer molecular weight, or the hydration shell (salting-out) of the cations. PEG 8000 and sodium sulfate formed the largest heterogeneous region, thus needing the smallest amount of phase-forming components for phase splitting. (C) 2016 Elsevier B.V. All rights reserved.