The oxidation of cyclohexane with H₂O₂ in a compressed CO₂/acetic acid binary system was studied at 60.0 and 80.0°C, at pressures up to 18 MPa, and with the zeolite TS-1 as catalyst. The phase behaviour of the reaction system was also observed. There are three fluid phases in the reaction system at lower pressure but two at higher pressures. In the three-phase region the yields of the products, cyclohexanol and cyclohexanone, increase considerably with increasing pressure and reaches a maximum near the phase-separating pressure. CO₂ can thus enhance the reaction effectively. However, the effect of pressure on the yield is very limited after the transition to a two-phase system.