The phase behavior of two types of polypropylene (PP) (commercial Ziegler-Natta PP and a metallocenic PP) in n-butane and in 1-butene is investigated in a high-pressure variable-volume view cell. For these systems, three types of phase equilibrium are observed: vapor-liquid, liquid-liquid and vapor-liquid-liquid. The statistical associating fluid theory equation of state (SAFT-EOS) is used to model the experimental data through bubble-point calculations. A simplified strategy to calculate the three-phase equilibrium in polymeric solutions via SAFT-EOS is presented. Results show a good agreement between the SAFT model and experimental data when a binary interaction parameter is employed to fit the experimental values. (C) 2001 Elsevier Science B.V. All rights reserved.