The molar excess enthalpies (H-E), at 298.15 K, of some mixtures of alkylbenzenes with n-heptane or cyclohexane were measured using a flow calorimeter. These data, along with the literature data on molar excess enthalpies (H-E), molar excess Gibbs energies (G(E)), molar excess heat capacity (C-p(E)) and activity coefficients at infinite dilution (gamma(i)(infinity)) of mixtures in n-alkanes or cyclohexane of mono-alkylbenzenes of general formula, C6H5-(CH2)(n-1)CH3, isomeric dimethylbenzenes (xylenes) and isomeric trimethylbenzenes were treated within the framework of DISQUAC, an extended group contribution model, in the simplified 'dispersive' version. The systems were characterized by three types of contact surfaces : phenyl (C6H5 group), alkane (CH3 or CH2 groups) and cyclohexane (c-CH2 group). The interchange energy parameters of the alkane/cyclohexane contacts were determined previously, the interaction parameters of the alkane/phenyl and cyclohexane/phenyl contacts are reported in this study. The dispersive parameters depend on the environment of the phenyl group and the number of alkyl groups adjacent to the phenyl group. The model provides a fairly consistent description of the experimental data as a function of concentration.