Vapor-liquid equilibria have been measured at 101.3 kPa for three binary mixtures of 2-butanone + t-pentanol, t-pentanol + butyl acetate and 2-propanol + diethyl ketone. The isobaric T-x-y data have been reported and the thermodynamic consistency has been examined. Calculations of the non-ideality of the vapor phase have been made with the second virial coefficients determined by the Tsonopoulos correlation. Various activity coefficient models have been used to correlate the experimental data. Satisfactory results have been obtained and optimally fitted binary parameters are presented.