In this work, the solute-solute interaction which exist in the CO2 + n-dodecane+ 3,7-dimethyl-1-octanol system was investigated. Solubility data were measured for three mixtures containing solvent free ndodecane fractions of 0.50, 0.75 and 0.85, between 308 K and 348K and pressures up to 14.9 MPa, with solvent mass fractions ranging from 0.375 to 0.984, using a static synthetic method. The data revealed significant solute-solute interactions, which resulted in the occurrence of co-solvency in the two n-dodecane rich mixtures. The phase behaviour data of the system was modelled, using the RK-ASPEN model. The modelling results indicated that, with the inclusion of a solute-solute interaction parameter, the fitted model was capable of correlating fairly accurate solubility data, but it can only approximate vapour-liquid-equilibrium data. (C) 2019 Elsevier B.V. All rights reserved.