Environmentally benign near-critical water offers substantial advantages over traditional organic solvents. In this work we use the hydrolyses of several substituted benzoate esters and a series of substituted anisoles as probes to elucidate the activity of the two ionic species in near-critical water. Each of these hydrolyses can run via both acid- and base-catalyzed pathways, as well as an S(N)2 pathway. An analysis of Hammett plots suggests that the benzoate esters hydrolyze autocatalytically, following an acid-catalyzed mechanism, whereas the anisoles are hydrolyzed via the S(N)2 mechanistic pathway. This work suggests that near-critical. water offers significant potential, both as a benign solvent and as a reaction medium that does not require neutralization with acid or base after the desired reaction is complete.