Densities of the carbon dioxide + n-decane binary system and carbon dioxide + n-decane + naphthalene ternary system have been measured up to 130 and 100 MPa, respectively, by using a vibrating tube densitometer. The measurements covered the molar compositions of CO2 of 0.1182, 0.3050, 0.6271, and 0.9539 for the first system, at temperatures from 318.15 to 358.15 K. While for the ternary mixtures, the measurements were performed for four compositions: high alkane, high aromatic, high CO2, and one equimolar content, at a temperature range of 328.15-423.15 K. From these data, excess molar volumes were calculated for both systems, showing positive values at lower temperatures and higher pressures for the binary mixtures, while negative values were observed for the ternary mixtures over the entire composition range. For both systems, the density was correlated by using a modified Tammann-Tait equation, as a function of temperature and pressure, presenting a maximum deviation of 0.63 and 1.72% for the binary and ternary systems, respectively. Additionally, isothermal compressibility and isobaric thermal expansivity were calculated from the experimental density data. It was observed that higher compressibility values were found at lower pressures and at higher CO2 content for both binary and ternary systems. Rich aromatic systems are less compressible when compared to rich CO2 systems. Regarding isobaric thermal expansivity, temperature dependence could be neglected for all binary mixtures. However, for the ternary mixtures, this dependence was strongly related to mixture composition.