||Capillary electrokinetic chromatography is a variant of capillary electrophoresis that uses a retentive phase in solution to facilitate the separation of neutral and charged species in the presence of an electric field. Some advantages of using electrokinetic chromatography include high speed analyses, high efficiency separations, and small amounts of sample and reagents required. One specific application of electrokinetic chromatography is for the indirect measurement of octanol-water partition coefficients (log P o/w ). The retention factor and log P o/w values of the test solutes are correlated for calibration purposes. Log P o/w values are accepted as a standard measure of hydrophobicity in the areas of pharmaceuticals, environmental, and the chemical industry. In this Work, three novel retentive phases have been evaluated for use in electrokinetic chromatography for the prediction of log P o/w values of small molecules with varying sizes and functional groups. One system chosen for study consists of a vesicle synthesized from oppositely charged surfactants. Cetyltrimethylammonium bromide (CTAB)-sodium octyl sulfate (SOS) vesicles provide rapid separations for determinations of log P o/w in the range of 0.5 to 5. A second type of retentive phase employed is a microemulsion consisting of heptane, 1-butanol, and sodium dodecyl sulfate (SDS) in buffer solution. This retentive phase is a highly versatile system, offering the separation of compounds in the hydrophobicity range of -1 to 7 log P o/w units. The third retentive phase system used for evaluation is an anionic, double chained surfactant that aggregates to form vesicles in saline solutions. Bis(2-ethylhexyl)sodium sulfosuccinate, also known as AOT, provides the efficient and rapid separation of solutes in the log P o/w range of 0 to 5.5. The separation of small organic molecules with a variety of functional groups and pesticide compounds were used to evaluate each retentive phase and compare the log P o/w calibrations. The three retentive phases are compared with regards to preparation, separation parameters and determination of octanol-water partition coefficients. The most versatile system for the determination of log P o/w values is the microemulsion phase. The retentive phase provides the broadest hydrophobicity range of analysis and closely resembles octanol-water partitioning without discrimination in separation.