The adsorption of 12 mono-, di-, and trichlorophenols from aqueous solutions on different activated carbons was studied. Distilled water and a minimal salt medium solution previously used in biotreatment studies with anaerobic organisms were used as solvents. A commercially available wood-based activated carbon (Chemviron carbon) and a lignite-based carbon produced at Queen＇s University were used as the adsorbents. The Chemviron carbon was used in both granular and powder forms. The adsorption data for each chlorophenol were regressed using the Freundlich equation. The fit was generally satisfactory, especially since the range of chlorophenol concentrations tested in this work extended over 6 orders of magnitude. The exponents of the chlorophenol concentration term in the Freundlich equations were found to be in the relatively narrow range 0.127-0.207. Therefore an attempt was made to regress all the data for all chlorophenols using a single isotherm, and a cumulative Freundlich isotherm was obtained. The Chemviron carbon was found to have a higher adsorbing capacity than the lignite-based carbon. The presence of additional inorganic solutes in the aqueous phase was found to have a negligible influence on adsorption.