more dense than the ethane-rich liquid over the entire threephase region. DATA ANALYSISIsothermal vapor and liquid composition data for the carbon monoxide-propane system were fitted to empirical equations in the form of power series in pressure. The mathematical form of the vapor and liquid polynomials, as well as the least-squares constants, are presented by Trust (7).The average standard deviation of the experimental liquid phase data from the curve was 0.28 mole % carbon monoxide. For the vapor phase the average standard deviation of the experimental data from the curves was 0.40 mole % propane.The experimental data for the carbon monoxide-ethane system were not fitted to equations. ACKNOWLEDGMENT