Isobaric vapor-liquid equilibrium (VLE) data were measured at 101.3 kPa by using an improved Rose equilibrium still for three binary systems, acetonitrile (1) + 1-propanol (2), acetonitrile (1) + dimethyl sulfoxide (DMSO) (3), and 1-propanol (2) + DMSO (3), and for one ternary system, acetonitrile (1) + 1-propanol (2) + DMSO (3). The VLE data of the binary systems were examined by thermodynamic consistency tests and satisfactorily correlated by Wilson and NRTL models. The parameters of two models obtained from the binary data were used to predict the ternary VLE data. The prediction yielded reasonable results for the ternary system.