Infrared spectroscopy was used to probe the interaction of CO2 under supercritical fluid (SCF) conditions with a fumed silica. The experimental difficulties associated with CO2 absorption of infrared light in the hydroxyl spectral region are overcome by using deuterated silica or by venting of the CO2 prior to obtaining a spectrum. It is shown that CO2 behaves quite differently from traditional nonaqueous solvents (i.e., carbon tetrachloride, toluene, and cyclohexane) with respect to interactions with the adsorbed layer of water on the surface. A dry silica easily extracts and adsorbs the residual water present in these nonaqueous solvents whereas, in contrast, a dry silica remains dry when placed in contact with the SCF CO2. Moreover, the CO2 extracts the adsorbed water from wet silica. The SCF solvent extracts more surface water into the fluid phase with increasing density, and repeated extraction cycles with SCF CO2 result in the removal of all water from the surface. The interaction of SCF CO2 with the hydroxyl groups was studied using deuterated silica. Using a dry or wet deuterated silica, the physisorption of CO2 with the isolated SiOD groups is shown to be weak in nature and of the same magnitude as that measured in CCl4. The SiOD band at 2762 cm(-1) is completely shifted to 2710 cm(-1) at relatively low pressures of CO2 (5 bar) and remains shifted with increasing amounts of CO2 up to the highest pressures studied (200 bar).