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. All 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 bill extremely time intensive W4 method.