The excess molar volumeVEof liquid mixtures of twon-alkane sis predicted essentially on the basis of the van der Waals model. The important feature of the treatment is thatVEmay be calculated from the respective desnsitis, isobaric expansivities and isothermal compressibilisties of the pure liquids, whereas data of solution properties need not be known. Neither any combining rules nor emprically adjusted parameters are used. Computed values are slightly less negative than the observed excess volumes, the average deviation being about 10%.