A simple apparatus for determining the critical points and vapor/liquid equilibrium curves is described. The apparatus was used to investigate pure CO 2, the binary system toluene-CO 2, and the ternary mixture toluene-H 2-CO 2. The critical points were obtained on the basis of both critical opalescence and isothermal compressibility. The critical temperature and critical pressure of CO 2 determined by this method agreed well with the literature values. The critical points of the binary and ternary mixtures were determined in CO 2-rich region. Peng-Robinson equation of state was used to predict critical points and the results agreed reasonably with the experimental data.