Solubility data are presented for a mixture of o-hydroxybenzoic acid (o-HBA) and m-HBA in supercritical CO2 doped with 3.5 mol % methanol. The data were measured at 318 and 328 K and for pressures in the range of 101-201 bar. Some new data for the solubility of pure m-HBA in methanol-doped supercritical CO2 are also presented. The solubilities of the HBA isomers are enhanced considerably with the addition of methanol to supercritical CO2. However, the solubility enhancement is strongly affected by the spatial arrangement of their functional groups (steric effect). There appears to be preferential interaction between the solutes and the cosolvent in the quaternary system, and this phenomenon is consistent with thermodynamic modeling of the system.