The adsorption of phenol and ten substituted phenols on activated carbon was examined. For a comparative study, the substituted phenols were selected after nature, position, and number of functional groups; they, are: o-,m-,p-cresol, o-,m-,p-chlorphenol, m-,p-nitrophenol, resorcine, and methyl-resorcine. p-chloraniline was also studied. The single solute data were statistically fitted on 13 isotherm models: the Freundlich, Langmuir, Freundlich-Langmuir, BET, Dubinin-Raduskevitch, the three parameters empirical equation proposed by Radke and Prausnitz, Redlich-Petersen, Tóth, Myers, as well as generalised, Volmer, virial and sigmoidal isotherms. A computer program was developed to determine the most precise parameter models. The prediction results on the adsorption isotherms are compared by absolute relative percent deviations.