An alkaline-side solvent extraction process was developed for cesium removal from Savannah River Site (SRS) tank waste. The process was invented at Oak Ridge National Laboratory and developed and tested at Argonne National Laboratory using single-stage and multistage tests in a laboratory-scale centrifugal contactor. The dispersion number, hydraulic performance, stage efficiency, and general operability of the process flowsheet were determined. Based on these tests, further solvent development work was done. The final solvent formulation appears to be an excellent candidate for removing cesium from SRS tank waste.