The Nitta-Chao EOS group-contribution model, based on cell theory, is used to study the interactions of the organic anhydride + n-alkane binary mixtures, A database of excess enthalpies, excess Gibbs energies and excess volumes for this kind of mixtures, together with molar volumes and vaporization enthalpies of pure organic anhydrides, were used to calculate the characteristic parameters of the Nitta-Chao group-contribution model. In order to enlarge the database, the excess molar volumes at 298.15 K for the binary mixtures of pentanoic and hexanoic acid anhydrides with an n-alkane are reported. An analysis of the interactions is presented with the estimation of the changes of the mean numbers of contacts between the different groups during the mixing process. The influence of the dispersive and non-dispersive interaction energy parameters on the excess volumes and excess enthalpies is also presented. The model consistently describes the experimental data of organic anhydride + n-alkane mixtures, i.e. the excess volumes increase when the anhydride chain length decreases and when alkane chain length increases. The symmetry of the V-E(x) curves and the sign and magnitude of the excess volumes are strongly dependent on the lengths of the alkane and of the organic anhydride,