A comprehensive study on the effect of hydrotropes such as urea, citric acid, sodium salicylate, and nicotinamide on the separation of phenol from phenol/o-chlorophenol mixtures under a wide range of hydrotrope concentrations, (0 to 3.0) mol.L(-1), and different system temperatures, (303 to 333) K, has been undertaken. The performance of hydrotropes toward separation of phenol was measured in terms of the Setschenow constant K(S). A Minimum Hydrotrope Concentration (MHC) in the aqueous phase was found essential to initiate significant separation of phenol from the phenol/o-chlorophenol mixture. The maximum enhancement factor which is the ratio of the percentage extraction value in the presence and absence of a hydrotrope has been determined for each case.