Clathrate phase equilibria for the ternary water-phenol-carbon dioxide system containing one-guest and two-host components were studied Three four-phase equilibrium loci for this ternary system were determined over wide temperature and pressure ranges. A quintuple point, thermodynamically unique, and invariant condition appeared in this type of ternary system, was carefully measured, and were 293. 7 K and 57.2 bar. At this quintuple point, five individual phases of water-rich liquid, phenol-rich liquid, carbon dioxide-rich liquid phenol clathrate, and vapor could coexist in equilibrium. A new experimental technique was used to determine the liquid-phase compositions coexisting with phenol clathrates at the isobaric conditions of 30.0 bar and six temperatures ranging from 278.2 and 303.2 K. A potential applicability of the clathration process to phenol separation from aqueous solutions was demonstrated in terms of phenol concentrations based on carbon dioxide-free concentration. In particular, phenol separation by using high-pressure carbon dioxide as a clathrate-inducing agent could be applied even to multiphase aqueous solutions over an entire range of phenol concentrations.