Physical adsorption on a silica gel (pore size of 80 nm, particle size of 10 m mu) has been studied for binary mixtures of methanol, acetone, and triethylamine diluted in supercritical CO2 by use of a FTIR transmission technique, Measurements were made at 313.2 K and pressures up to 15 MPa. Vibrational frequencies of hydroxyl groups on the silica gel surface shift downward due to the hydrogen-bond formation with organic substances, As the pressure increases from 0.1 MPa, the integral absorbance of the hydrogen-bonded OH groups interacting with methanol or acetone increases at first, and reaches a maximum at a pressure below the critical pressure of CO,, and then the intensity decreases gradually with increasing pressure, Furthermore, both spectra of hydrogen-bonded OH groups of silica and C = O group of acetone show a slight frequency downshift with increasing pressure, On the other hand, the integral absorbance for triethylamine in CO2 is almost constant from 0.1 to 15 MPa, indicating that most of the surface OH groups are covered by triethylamine molecules.