Vapor-liquid equilibria were measured at 101.3 kPa for three binary mixtures of cyclopentane + isopropyl acetate, isopropyl acetate + hexane, and cyclopentane + methylmethacrylate. The isobaric T-x-y data were reported, including an azeotropic point for the binary mixture of isopropyl acetate + hexane. Calculations of the nonideality of the vapor phase were made with the second virial coefficients determined by the Tsonopoulos correlation equation. Various activity coefficient models were used to correlate the experimental data. Satisfactory results were obtained, and optimally fitted binary parameters are presented.