pH has been shown to have an effect on the direct supercritical-fluid extraction of phenol and 2,4,6-trichlorophenol from aqueous samples. pH affects both extraction efficiencies and extraction kinetics,but the extraction pressure also plays an important role. By altering the pH the amount of neutral analyte as well as the speed at which the analyte is extracted from aqueous samples can be greatly affected. A change in pH appeared to exhibit the largest effect when the extraction pressure was 150 atm for either phenol. By increasing the extraction pressure to 300 atm, the importance of pH on extraction efficiency decreased. The production of carbonic acid when employing carbon dioxide as the extraction fluid for aqueous extraction makes this an advantageous circumstance for the extraction of phenols and other acidic compounds, whereas it may become problematic for basic compounds by increasing the extent of ionization of the basic compounds.