Practical LLE systems contain an aqueous and organic phase where, after splitting, the dense organic phase is referred to as the third phase. In this study we consider just the organic phase such that the associated phase transition is from one phase to two. Third phase formation is widely associated with organic phase separation upon cooling; Figure shows the T-φ E diagram with this upper critical solution temperature (UCST) behavior. We consider two extractants: DMDBTDMA and DMDBPMA, shown in Figure . The former is commonly applied to rare earth separations while the latter is a more hydrophilic analog that has been used to investigate the role of extractant lipophilicity. As illustrated in the schematic phase diagrams in Figure , organic phase mixtures are prepared with φ E increments of 0.10 for combinations of DMDBPMA with hexane, octane, decane, dodecane and hexadecane, and DMDBTDMA mixtures are prepared with dodecane.