The phase behavior of a system of importance for the hydroformylation reaction of 1-hexene in supercritical CO2 has been studied in the range of 303.2-348.2 K with different CO2 mole fractions. The conversion of 1-hexene varies from 0 to 1. The density of the reaction mixture at different conditions are also determined. It is demonstrated that the phase behavior changes with conversion of 1-hexene. At zero conversion, the phase separation pressure increases with increasing concentration of the reactants in the reaction system and decreases slightly with the increase of temperature. At other conversions, the phase separation pressure increases as temperature rises. The density of the reaction mixture at phase separation point is higher at the larger conversions. (C) 2003 Elsevier B.V. All rights reserved.