The dipolarity/polarizability parameter, pi*, of Kamlet and Taft is used to characterize the solvent properties of CO2/1,1,1,2- tetrafluoroethane (HFC134a) mixtures in the supercritical state. It is shown that: preferential solvation of the solute by HFC134a occurs. The local composition of the polar constituent is shown to steadily decrease as the pressure is increased, but: the local pi* value does not decrease below that of the bulk fluid. A mixture of 30 mol % HFC134a in CO2 has properties similar to these of bulk HFC134a at high densities. Such a mixture is extremely useful for extraction purposes, as it has a critical temperature that is 42 degrees C lower than bulk HFC134a.