Accurate experimental values for the free energies of hydration, or the free energies of solvation, of the H+. OH-, and H3O+ ions are of fundamental importance. By use of the most accurate value for the free energy of solvation of H+, the known value for the free energy of solvation of water, and the known values for the gas phase and aqueous phase deprotonation of water, the corresponding experimental free energy of solvation for OH- is -106.4 +/- 0.5 kcal/mol. Similarly, by use of the known values for DeltaG(f)(0) for H3O, H2O+, and OH-, the known values for DeltaG(s) for H+ and OH-, and the known value for the aqueous phase autoionization of water, we obtain an experimental free energy of solvation value for H3O+ of -103.4 +/- 0.5 kcal/mol. These values are in excellent agreement with the commonly accepted values and with the value for DeltaG(s),(OH-) obtained from embedding, clusters of OH-(H2O)(n) in a dielectric continuum.