The vapour-liquid equilibria of the binary systems perfluoromethylcyclohexane-pentafluorobenzene, benzene-pentafluorobenzene, benzene-methylperfluorobutanoate and perfluoromethylcyclohexane-methylperfluorobutanoate have been measured at 333.07 K and 343.12 K using a dynamic circulation still of the Sieg-Rock type. The thermodynamic consistency of the measurements was tested by two different methods. New UNIFAC interaction parameters [1] were calculated for the following groups: ACH-ACF, ACF-CF2, CF2-COO, ACCH(2)-ACF, ACH-CF2. The abbreviations stand for the following increments: ACH = aromatic CH group, ACF = aromatic CF group, CF2 = aliphatic CF2 group, COO = ester group and ACCH(2) = side chain CH group.