The atomization energy and structure of SO3 have been calculated using the advanced ab initio method, CCSD(T), in combination with the newly revised families of correlation consistent basis sets, cc-pV(n + d)Z and aug-cc-pV(n + d)Z (where n = D(2), T(3), Q(4), or 5). The impact of these sets upon structure and energy has been examined, as has convergence behavior toward the complete basis set (CBS) limit. Overall, these revised sets have a particularly strong effect upon energies determined using the lower level basis sets, and can reduce the unusually large deviation from experiment by over half.