The liquid-liquid-vapor (L1L2V) phase boundaries of solvent(s)-CO2-heavy oil systems under reservoir conditions are experimentally and theoretically determined. Experimentally, the L1L2V phase boundaries of one CO2-heavy oil mixture, one C3H8-CO2-heavy oil mixture, and one n-C4H10-CO2-heavy oil mixture in the pressure temperature (P T) diagram are determined using a versatile pressure-volume-temperature (PVT) setup. The addition of an alkane solvent to the CO2-heavy oil system tends to expand the pressure and temperature span of the L1L2V phase boundary, while the L1L2V phase boundary of the solvent(s)-CO2-heavy oil system shows its tendency to move toward the high-temperature and low-pressure region of the P-T diagram. Theoretically, the previously developed binary interaction parameter (BIP) correlations for CO2-heavy oil binary, C3H8-heavy oil binary, and n-C4H10-heavy oil binary are incorporated into the Peng-Robinson equation of state (PR EOS) to determine the three-phase boundaries of the above-mentioned systems. The PR EOS with a modified alpha function and the BIP correlations is found to provide a generally good prediction of the experimentally measured L1L2V phase boundaries of the solvent(s)-CO2-heavy oil systems under reservoir conditions.