Hydroquinone was used to form clathrate compounds with binary (CO2 + CO) gas mixtures of various compositions at two experimental pressures (2.0 and 4.0 MPa). According to the spectroscopic measurements, both CO and CO2 molecules were found to be captured in the clathrate cavities. However, enclathration of CO2 rather than CO was more likely regardless of the gas composition. Numerical integration and elemental analysis indicate that the process for enclathration of CO2 molecules is saturated when the CO2 mole fraction is 0.6 or larger. Occupancy was found to be 100% at 4.0 MPa and similar to 70 - 80% at 2.0 MPa. Even though all the cavities seemed to be filled with CO2 molecules, a CO-clathrate signal could still be observed from the C-13 NMR spectroscopy. This might result from the non-stoichiometry of clathrate compounds. Because the separation efficiency of CO2 is significantly higher than that for CO, even at the lowest CO2 concentration in the gas phase, a clathrate-based process can be designed to separate CO2 from binary (CO2 + CO) gas mixtures.