Equilibrium phase compositions (TPXY) are measured in a flow cell apparatus for a bitumen + decane + CO2 system. Statistical Associated Fluid Theory (SAFT) [Huang, S.H. and Radosz, M., 1990a. Fluid Phase Equilibria, 60 : 81-98; 1990b. Ind Eng. Chem. Res., 29 : 2284-2294] and Peng-Robinson equations of state are found to give similar results for the condensed phase compositions. However, SAFT is found superior in predicting the supercritical fluid phase compositions. Hence, the bitumen partitioning coefficients (K-factors) can be reliably predicted with SAFT but not with PR. Moreover, the SAFT characterization approach based on measurable molecular properties is more appropriate for heavy, associating bitumen components than is the PR characterization approach based on hypothetical critical properties. Finally, SAFT-predicted K-factors allow for quantifying cosolvent selectivity and capacity in fractionating bitumen with supercritical CO2.