As mentioned earlier, one of the biggest modern developments in accelerating quantum chemistry calculations are density fitting approximations. These require one or more auxiliary basis sets, which typically must be optimized for each orbital basis set, which itself is different for each method. In particular, the fitting sets used for the Fock matrix integral fitting have different requirements to those used for fitting the transformed, molecular integrals in correlated methods. There have been a number of heuristic approaches suggested for automatically generating auxiliary basis sets, but these all necessarily produce overly large sets, so as to avoid large fitting errors. As even a well-optimized fitting set can be 2 or 3 times the size of the orbital set, there are many instances where such unoptimized fitting sets may become a computational bottleneck. However, the process for optimizing these sets Results are across all test molecules, using the optimized JKFit auxiliary basis sets for cc-pVnZ orbital sets (n = T, Q, 5) for the first three noble gas atoms.