Supercritical fluid technologies as alternative methodologies to conventional procedures are being explored for the direct extraction of acidic and polar contaminants from aqueous matrices. In support of the knowledge required to implement these novel methods, the partitioning of pentachlorophenol between water and liquid and supercritical CO2 has been characterized by determining distribution coefficients at (18.8, 41.7, and 59.8) degrees C from a saturated water solution (11.6 x 10(-6) g/g solvent). The partitioning of pentachlorophenol from dilute solution (1.27 x 10(-6) g/g solvent) was measured at (42.2 and 59.9) degrees C. Distribution coefficients were lower at this reduced concentration. Measurements were made at pressures up to about 280 bar. Comparison of the partitioning data to the solubility ratio of the solute in both phases contributes to the interpretation of relevant interactions in this complex system.