Surfactants are industrially important ingredients because of various applications in cosmetic,pharmaceutical,and food industries.Especially,ethoxylated alcohol {H-(CH2)i-(OCH2CH2)j-OH or CiEj} surfactants are a particularly interesting class of nonionic surfactant because they have both ether (-O-) and hydroxyl (-OH) groups in a single molecule.As a consequence,mixtures of CiEj with hydrocarbon or alcohol solvents tend to easily associate.But only a few data are available for (nonionic surfactant + hydrocarbon and alcohol) systems,whereas phase equilibrium data for (surfactants + water) systems under atmospheric pressure have abundantly been published.Accordingly,our previous studies focused on isobaric vapor-liquid equilibrium (VLE) [1-4] and isothermal VLE [5,6] experiments for binary systems of (nonionic surfactants + hydrocarbon or alcohol) mixtures.This study presents isobaric VLE data for the binary system of alcohol and ethylene glycol monopropyl ether (C3E1).This system possesses many kinds of associating pairs in it and hence shows highly non-ideal phase behavior due to the hydrogen-bond interaction.The experiments on this system were carried out at different constant pressures using the Fischer VLE 602 apparatus.Consistency of the measured data was tested by the Fredenslund’s and Wisniak’s verification methods,and the data were confirmed to be thermodynamically consistent.Correlation of the measured data was attempted by using a two-term virial equation for vapor-phase fugacity coefficients and by using the Wilson,NRTL,and UNIQUAC EOS for liquid-phase activity coefficients.The correlated model shows a good agreement with the measured data.