A representation of binary CO 2 /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 CO 2 : chain length m, segment diameter σ, and interaction energy /k. Assuming that n-alkanes are made of identical segments ( /k and σ independent of carbon number n C ) but in different number, only three parameters were necessary for the whole n-alkane series (m is linearly correlated to n C ). Two additional binary interaction parameters k ij and l ij 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 CO 2 /branched alkane binary systems is also presented.