Abstract The effect of pressure on the solvolysis rates of representative primary, secondary, and tertiary tosylates was investigated in three representative solvents—formic acid, aqueous acetone, and methanol. The calculated activation volumes for these reactions were found to depend on the substrate structure and on the nature of solvent in a systematic manner. The activation volumes for kc-like reactions were less negative than those for ks-like reactions. In the case of the nearly ks-like reactions, the activation volume was found to be governed by the partial molal volume of the initial state.