The constant volume heat capacities (C-V) of CO2, propane-CO2, n -pentane-CO2, n -heptane-CO2, acetone-CO2, and ethanol-CO2 were measured at 308.15 K in the pressure range from 6 to 11 MPa, and the concentration of the solutes was 0.5 mol%. The results show that there is a maximum in each C-V versus pressure curve which occurs at the pressure where the isothermal compressibility k(T) is largest. The peak in the C-V curve of propane-CO2 is higher than those of n-pentane-CO2 and n-heptane-CO2 Mixtures. For the mixtures with polar solutes, the magnitude of the peaks in C-V curves is nearly the same although the structure and polarity of the solutes are different. The intermolecular interaction in the mixtures is discussed on the basis of the C-V. (C) 2002 Elsevier Science B.V. All rights reserved.