A high-pressure phase behavior apparatus is presented in this paper. One new feature of the apparatus is a "rodded cylinder", which greatly simplifies the equipment design. This experimental apparatus is capable of performing vapor-liquid equilibrium tests at pressures up to 40 MPa and temperatures up to 150 degreesC. Test runs of the apparatus have been made to study the phase behavior of CO2-containing binary and ternary fluid mixtures. The measured compositions of equilibrium vapor and liquid phases are in good agreement with those reported in the literature. This apparatus is useful for generating data required for process designs of supercritical fluid extraction.