A head-space technique has been used to determine vapor-phase equilibria for binary mixtures of linear or cyclic mono- and polyalkenes + n-alkanes or + cyclohexane. Excess molar Gibbs energies, G(E), for the mixtures investigated were obtained by a least-squares treatment of the equilibrium results. These data, the previously measured excess enthalpies, H-E, and the data available in the literature on G(E), H-E, activity coefficients at infinite dilution, gamma(i)(infinity), and molar excess enthalpies at infinite dilution, h(i) (E,infinity) are examined on the basis of the DISQUAC group contribution model. The model provides a fairly consistent description of the phase equilibria and the related excess functions, using a unique set of structure-dependent dispersive parameters.