Gas-phase deprotonation enthalpies were measured for chloric and perchloric acids and found to be 313.2 ± 3.3 and 299.9 ± 5.7 kcal mol -1, respectively. These values were combined with the previously reported electron affinities of ClO3 and ClO4 to obtain BDE(H-OClO2) = 97.6 ± 4.0 kcal mol-1 and BDE(H-OClO3) = 107.4 ±6.1 kcal mol-1. These energetic determinations represent the first measurements of these quantities or extensive revisions of the currently available values. B3LYP, M06, M06 - 2X, G3, and G3B3 computations also were carried out to provide acidities, electron affinities, bond dissociation energies, and heats of formation via atomization energies for ClOx and HClOx, where x = 1 - 4. AU of the methods do a reasonable job for the first three thermodynamic quantities but only M06 does a satisfactory job for the heats of formation, and its performance is similar to the highly accurate but extremely time intensive W4 method.