The group contribution approach of Elvassore et al. [Ind. Eng. Chem. Res. 38 (1999) 2110] has been used in combination with the cubic EoS of Sako-Wu-Prausnitz (SWP) to determine the three characteristic parameters of this EoS for the carbonate group, with the aim to describe the thermodynamic behaviour of carbonate type compounds. For this purpose a database containing compressed and saturated liquid densities of dimethyl carbonate and diethyl carbonate was used. Two options were considered in order to choose the contributing functional groups in carbonate molecules. First these molecules were considered as formed by methyl, methylene and carbonate groups, defined as CH3, CH2 and OCOO, respectively, but the results obtained were not satisfactory. Then in a second step, the carbonate compounds were considered formed by CH3, CH2, CH3alpha, CH2alpha, and OCOO groups, taking into account the proximity effect of the oxygen atom over the neighbouring methyl and methylene groups. This last option presented deviations much lower than the first one. From the parameters calculated in this work for CH3alpha, CH2alpha and OCOO, and those determined by Elvassore et al. for CH3 and CH2 groups the vapour-liquid equilibria and PVTx values for dialkyl carbonate + n-alkane systems have been calculated and compared with the available experimental literature data. (C) 2003 Elsevier Science B.V. All rights reserved.