Relative gas-phase stabilities of 25 kinds of ring-substituted phenoxide anions were determined theoretically using proton transfer reactions. The energies and geometries of phenoxide anions and their corresponding phenols, which are involved in the reactions, were calculated at the B3LYP/6-311+G(2d,p) level of theory. The comparison of the obtained substituent effects with those of benzylic anions revealed that the stabilities of phenoxide anions were governed by the inductive effect and two additive effects of ring substituents in a manner similar to that of benzylic anions. Statistical analyses elucidated that the behavior of the substituent effects of phenoxide anions as well as benzylic anions can be described quantitatively by three terms using an extended Yukawa-Tsuno equation: . Through examinations of the structural changes and charge distributions in the anions, these additional effects were identified as the resonance and saturation effects, which stabilize anions by the para + R groups and the electron-releasing groups, respectively. Copyright © 2012 John Wiley & Sons, Ltd.