A new vapor liquid double recirculation apparatus was developed for use with complex (continuous) mixtures. The apparatus features on-line simulated distillation chromatography for analyzing both vapor and liquid phases. The simulated distillation analysis provides a cumulative boiling point curve which is a continuous representation of the composition distribution of the heavy fraction in a semi-continuous mixture. Experimental data are presented for two systems : CO2 + a light distillate, and CO2 + a whole stock-tank oil. The experimental composition distributions are compared with those predicted from the continuous Peng-Robinson EOS formulation of Haynes and Matthews.