Cloud point isopleths, bubble-point isopleths and liquid-liquid-vapour bubble point isopleths were measured for a binary system of linear low density polyethylene (LLDPE) and n-hexane and for the ternary system LLDPE + n-hexane + ethylene. The experiments were performed according to the synthetic method in the temperature range 400-500 K and at pressures up to 14 MPa. The LLDPE used was a hydrogenated polybutadiene and was almost monodisperse (M-w/M-n = 1.19). Measured experimental data for the system LLDPE + n-hexane and experimental data for the system LLDPE + ethylene taken from literature [H. Trumpi, Th.W. de Loos, R.A. Krenz, R.A. Heidemann, High pressure phase equilibria in the system linear low density polyethylene + ethylene: experimental results and modeling, J. Supercrit. Fluids 27 (2003) 205-214.] were modelled with the modified Sanchez-Lacombe equation of state. The same LLDPE sample was used in both experiments. The parameters for LLDPE were found by performing a sequence of non-linear regressions on pressure-volume-temperature reference data for molten polyethylene and the experimental cloud point data for the systems LLDPE + n-hexane and LLDPE + ethylene. From this information and a Sanchez-Lacombe fit to n-hexane + ethylene data the phase behaviour of the ternary system LLDPE + n-hexane + ethylene can be predicted. Using this procedure the influence of the ethylene concentration on the cloud point pressure is slightly under predicted. Therefore, the LLDPE-ethylene binary interaction parameter was adjusted to ternary LLDPE + hexane + ethylene cloud point data. In this way the modified Sanchez-Lacombe equation gives a very good description of the ternary cloud point curves and an almost quantitative prediction of the ternary bubble point and liquid-liquid-vapour boundary curves. (C) 2005 Elsevier B.V. All rights reserved.