The molecular formulas and charge state distributions of thus-far known ubiquitous alkanethiolate-protected gold clusters with core-masses of 8 and 29 kDa were assessed using electrospray ionization mass spectrometry. The 8 and 29 kDa clusters were determined to be composed of single species, [Au-38(SCn)(24)](z) and [Au-144(SCn)(59)](z), respectively, with charge states of z >= 0. Possible geometric structures for Au-38(SCn)(24) and Au-144(SCn)(59) are discussed, based on the structures of relevant systems that have been recently determined experimentally and theoretically: [Au-25(SR)(18)](-) and Au-102(SR)(44), in which the Au cores are protected by monomers [-SR-Au-SR-] and/or dimers [-SR-Au-SR-Au-SR-]. Their preferential formation and chemical robustness are proposed as being associated with high stability due to geometric factors, while the Au-thiolate interface takes on common motifs regardless of the underlying Au core.