A one-pass flow system for the determination of the solubilities of solids and liquids in compressed gases is described. The solubilities of styrene in supercritical carbon dioxide ar different conditions are determined. The range of temperatures covered is 323-333 K and pressures 8.0-24.0 MPa. An equation representing solubility behavior is derived from the solvation concept, the equilibrium constant of the high pressure reaction and the rules of the phase equilibrium. This is compared with the experimental results, and very good agreement is obtained. Some experimental results from the literature are also reproduced by means of this equation, and very good agreement with these experimental results is found, as in previous examples. Agreement between values of a(0), obtained from parameter fitting by this equation and those from the literature is very good. The relation between the parameter a(1), of the equation and the second virial coefficients is also discussed.