Kinetics of oxidation of thioethers, alkenes, and sulfoxides by tetrahexylammonium tetrakis(diperoxomo1ybdo) phaephate (TEAM) were performed in chloroform. The results obtained, compared with the correaponding data of a series of Mo(V1) peroxo complexes, rule out a nucleophilic oxygen transfer mechanism. Rather, the data point to Mo(VI) peroxopolyoxo complexes as well as simple peroxo complexes behave as electrophilic oxidants toward nucleophilic substrates such as thioethers and alkenes. A study of the countercation effects indicates that the increasing bulkiness of the cation reduces the electrophilicity of the peroxopolyoxo complex. With sulfoxides, incursion of SET processes might be a likely event.