Vapor-liquid equilibria were measured at 101.3 kPa for the three binary and one ternary mixtures of cyclohexane, 3-methyl-2-butanone, and octane. The isobaric T-x-y data were reported, including an azeotropic point for the binary mixture cyclohexane + 3-methyl-2-butanone, The virial equation of state truncated after the second coefficient was used to calculate the vapor-phase fugacity coefficients. The Tsonopoulos correlation equation was applied to determine the second virial coefficients. Various activity coefficient models of the Wilson, the NRTL, and the UNIQUAC equations were used to correlate the binary experimental vapor-liquid equilibrium results. Optimally-fitted binary parameters of the activity coefficient models were obtained and those paramters of the NRTL model were employed to predict the ternary vapor-liquid equilibria. Satisfactory results were presented for the correlation and prediction of the vapor-liquid equilibrium data on binary and ternary mixtures.