The characteristic parameters for the Tassios et al. (Ind. Eng. Chem. Process Des. Dev. 23 (1984) 391; 24 (1985) 701; 25 (1986) 22), Larsen et al. (Ind. Eng. Chem. Res. 26 (1987) 2274), and Gmehling et al. (Ibid. 32 (1993) 178) versions of UNIFAC model for organic anhydrides + n-alkane systems have been calculated. For the first time, published data on excess enthalpies have been used to estimate the interaction parameters between the anhydride group CO-O-CO and the methyl and methylene groups (CH3 and CH2), respectively. In the case of the Gmehling version, the geometrical parameters of the anhydride group are also determined. The mean deviations for the excess enthalpies were about 2% for all versions. We have also compared our results with those obtained by Kehiaian et al. (Fluid Phase Equilibria 69 (1991) 91) with the DISQUAC model.