The solubility of carbon dioxide in poly (ethylene terephthalate) (PET) at high pressure and elevated temperature conditions was investigated for a better understanding of the phase equilibrium characteristics of supercritical CO2/PET binary system and useful data for the process development of the supercritical fluid dyeing. Based on the principle of pressure decaying, a novel experimental apparatus suitable to high pressure and high temperature measurement was established. The solubilities of CO2 in PET were measured with the apparatus at temperatures of 110, 120, and 130 degrees C and pressures up to 30.0 MPa. The results show that the solubility of CO2 in PET increases with the increase of pressure and CO2 density, respectively, at a constant temperature, whereas it decreases with the increase of temperature at a constant pressure. The Sanchez-Lacombe equation of state (S-L EOS) was used to correlate the experimental data. The calculated results are in good agreement with the experimental ones. The average absolute relative derivation (AARD) is less than 3.91%. (C) 2008 Wiley Periodicals, lnc.