A simple apparatus for determining critical points is described. The apparatus was used to investigate pure CO2, the binary system of toluene-CO2, and the ternary system methylcyclohexane (MCH)-H-2-CO2. The critical points were obtained on the basis of both critical opalescence and the appearance of the meniscus at equal volume of vapor and liquid. The critical points of pure CO2 and the toluene-CO2 system determined by this method agreed well with the literature values. The critical points of the ternary system MCH-H-2-CO2 were determined in the CO2-rich region. The Peng-Robinson equation of state was used to predict the critical points and the results agreed reasonably well with the experimental data.