The solubilities in binary and ternary systems of hydroquinone (1,4-dihydroxybenzene) and p-quinone (1,4-benzoquinone) in supercritical carbon dioxide were measured in the pressure range 10.0 to 35.0 MPa at temperatures of 333, 348 and 363 K. In binary systems, the solubility of hydroquinone was three orders of magnitude lower than that of p-quinone. This difference in solubility was lower in the ternary system because the solubility of hydroquinone increases, while the solubility of p-quinone decreases. The measured solubilities in the binary and ternary systems were correlated using a semiempirical model proposed by Bartle.