Abstract: Vapor-liquid equilibrium data for the system chlorodifluoromethane at 254.64, 272.75, 283.03 and 293.33 K were determined with a vapor phase circulation apparatus. Equilibrium data at the four temperatures have been correlated and predicted by calculating the fugacities of the liquid and the vapor simultaneously with the Martin-Hou (81) equation of state. The unique features of the apparatus in vapor circulation, auto-compensation for volume and continuous in-line sampling and analysis of both the vapor and the liquid phases insured the reliability of the measurements.