Supercritical fluids (SCF) have become increasingly popular, especially as extraction solvents. Already, General Foods uses SCF carbon dioxide to extract caffeine from coffee beans and the EPA is experimenting with the use of SCF's to clean up contaminated GAC, soils and sludges. Basic understanding of the thermodynamics of SCF's is, however, still lacking so that these important processes continue to be designed at least somewhat empirically. The most striking contribution from my prior research is the development of a spectroscopic technique that showed greatly enriched local densities of SCF solvents around solutes when operating in the region near the critical point. This was the first evidence of its kind to support the idea that "clustering" occurs in SCF's even when both the solvent and the solute are nonpolar. The PI believes that this clustering and other specific chemical interactions are the main components missing in traditional equation of state models that, unfortunately, are not able to accurately predict SCF phase behavior.