Using quantum chemical methods, the thermodynamic stabilities of benzoic, o-, m-, and p-hydroxybenzoic, and acetic acids and their conjugate bases were studied in both gas phase and aqueous solution, enabling the computation of the pK(a)'s of the above acids. The electronic structure calculations were carried out at the Hartree-Fock SCF and MP2 levels of theory, using 6-31G(d,p) and 6-311+G(2d,p) basis sets. Solvation energies were calculated using two dielectric continuum methods : SCIPCM and PCM. o-Hydroxybenzoic acid and its anion were found to possess intramolecular hydrogen bonds, which in the case of the anion are so strong as to result in a "bridged" structure in the gas phase with the proton effectively midway between the oxygens of the carboxylic and hydroxide groups. As a consequence of this strong hydrogen bond, the ortho anion appears to have the lowest solvation energy, lower (in magnitude) by similar to 8-10 kcal/mol than that of benzoate itself, despite the presence of a potentially hydrophilic hydroxy group, The trends in the calculated solvation energies of the anions provide an explanation for the unusual binding strength of o-hydroxybenzoate to surfactant films. The computed pk(a)'s of the acids were analyzed in terms of the contributing energetics, and while these calculations have not yielded quantitatively accurate predictions of the pk(a)'s, they do exhibit the correct qualitative trend among the acids studied.