A representation of binary CO2/n-alkanes (n-C-3 to n-C-44) systems series using a SAFT equation with molecular assumptions is presented below. A minimum number of parameters were adjusted, which is eight in this case. Three parameters are required for pure CO2: chain length m, segment diameter sigma, and interaction energy Elh. Assuming that n-alkanes are made of identical segments (epsilon/k and a independent of carbon number no) but in different number, only three parameters were necessary for the whole n-alkane series (m is linearly correlated to no). Two additional binary interaction parameters k(ij) and lu were used to model the mixtures. The van der Waals one fluid model was used with k(ij) and l(ij) independent of temperature and chain length. The agreement between calculated and measured total and partial pressures is satisfactory (within 8%) in view of the experimental accuracy and the very restrictive assumptions made. Finally, an extension to CO2/branched alkane binary systems is also presented.