Abstract The measurement of equilibrium dye uptake in PET fiber is carried out using a flow-type cylindrical vessel. Using the expanded liquid model in which both phases are supposed to be liquid mixtures, the equilibrium uptake of C.I. disperse red 60 may be calculated from each binary interaction parameter of carbon dioxide–dye, carbon dioxide–PET and dye–PET binary systems. The calculated uptake is compared with the observed one with the same order of magnitude, even though the former is overestimated. The binary interaction parameter of dye–PET system that is obtained from the equilibrium dye uptake in PET is smaller by about 1.5 than that obtained by the binary system. Nevertheless, it is found that the predicted uptake of dye with using the interaction parameter regressed from the ternary data is in excellent agreement with the experimental one. The distribution of C. I. disperse red 60 into supercritical fluid and PET phase at equilibrium can be predicted and compared with the experimental one. The estimated distribution coefficient increases with the pressure increase, because the sorption of dye in PET fiber increases slowly with the pressure than the dye solubility in carbon dioxide does. This tendency is weakened with increase of temperature.