The cesium distribution coefficients for extraction, scrubbing, and stripping of the caustic-side solvent extraction flowsheet were measured for a number of tank waste supernates from both the F- and H-Area Tank Farms. The measured distribution coefficients, D(Cs)s, indicate that the caustic-side solvent extraction flowsheet will successfully decontaminate the supernate and produce a concentrated, dilute nitric acid product. Because of the difficulty in performing the experiments on a 40-mL scale in the shielded cells, some caustic carryover into the scrub acid occurred and contributed to the higher-than-expected scrub distribution coefficients.Comparing the measured extraction distribution coefficients to recently published data by Oak Ridge National Laboratory (ORNL) personnel showed agreement between the model and experiments with two actual tank wastes. However, tests with three other tank wastes gave extraction D(Cs)s that deviated from the model predictions. Additional refinements of the model are planned in FY 2002. Two of these measurements were below the flowsheet requirement for extraction. Several aspects of the waste chemistry (e.g., anion concentrations) were examined; however, no distinct correlation was found for extraction distribution coefficient behavior.Testing also examined the affinity of the calixarene-solvent system for actinide removal. Plutonium and uranium extraction distribution coefficients measured around 2. However, additional analytical work is needed to measure the mass of the actinides in the organic phase (Wilmarth, W.R., Hobbs, D.T. Task Technical and Quality, Assurance Plan Supporting CSSX Pilot Plant Critically Issues; WSRC-RP-2001-0076; Westinghouse Savannah River: Aiken, SC, 2001).