Isothermal vapour-liquid equilibrium was measured for the systems of diethyl sulphide + 1-butene, +cis-2-butene, and +2-methylpropene at 312.6K, diethyl sulphide + n-butane was measured at 317.6K, diethyl sulphide + trans-2-butene at 317.5K, and diethyl sulphide + 2-methylpropane at 308.0K. The pressure-temperature-total composition data were converted into pressure-temperature-liquid-vapour composition data using the method of Barker. Error estimates are provided for each variable. The isothermal parameters for the Wilson, NRTL and UNIQUAC activity coefficient models were regressed. The measurements were compared with the predictions by COSMO segment activity coefficient (COSMO-SAC) and UNIFAC. (C) 2010 Elsevier B.V. All rights reserved.