Single-solute sorptions onto the organically modified montmorillonite were completed at 2 different pH conditions, 7 and 11.5, in a batch reactor to investigate the pH-dependent uptake of 2-chlorophenol (ChP), 3-cyanophenol (CyP), and 4-nitrophenol (NiP) dissolved in water at 25 degreesC. During the preparation of HDTMA-clay, hexadecyltrimethylammonium (HDTMA) cation was exchanged for metal cations on the montmorillonite at the cation exchange capacity of the montmorillonite. During the process, the montmorillonite changed from having a hydrophilic to an organophilic surface. Experimental results show that the sorption affinity on HDTMA-clay was in the order of 2-ChP > 4-NiP > 3-CyP for the 2 pH conditions. The Langmuir and the Redlich-Peterson (RP) models were used to fit the single-solute sorption equilibria data graphically. The ideal adsorbed solution theory (LAST) coupled with a single-solute model (i.e., either Langmuir or RP model) was used to predict the multisolute competitive-sorption equilibria. Predictions from the IAST at each pH condition yielded favorable representations of multisolute competitive sorption of the phenolic compounds onto HDTMA-clay.