512The interest in supercritical fluid (SCF) solvents in chemical reaction processes derives from both their participation in reactions as well as their pressure-dependent solvent effects. Herein are described: (1) a set of hydrolysis reactions of aryl-alkyl ethers in supercritical water; (2) the influence of SCF solvent effects on rate constants; (3) a contrived example of the influence of SCF illustrating the compromise between (1) and (2) that can lead to the specification of an optimal SCF solvent; and (4) a real example of the enhancement of shale oil upgrading in the presence of supercritical H2O and HCl.