In this work, modelling of the phase behaviour in ternary systems composed of CO2 + n-alkanes + 1-alkanols is described. The model assumes that the ternary system is congruent to binary systems composed of CO, + n-alkanes and that the phase behaviour of the ternary system can be related to the average molecular size of the solute molecules. The average molecular size of the solute molecules is calculated taking into account alkanol aggregation. Although some crude assumptions have been made, the model is able to describe experimental results qualitatively. Values for model parameters like the degree of aggregation and the equilibrium constant of the aggregation reaction correspond very well to values for these parameters obtained from IR-spectroscopy.