Binary infinite-dilution activity coefficients and LLE data for 14 systems (five aqueous systems, five alcohol + hydrocarbon systems, acetonitrile + n-hexane, and three nitroethane + hydrocarbon systems) are simultaneously correlated with a modification of the extended UNIQUAC model, which also reproduces well binary and ternary VLE data for mixtures containing methanol + +n-pentane bordering on liquid-liquid immiscibility.