The reaction of the tetraperoxomolybdate dianion, Mo(O2)42−, with thioanisole, PhSMe, in reverse micelles of cetylpyridinium chloride (CPyCl), in CHCl3 is initially first-order in each reactant, indicating that this reaction involves direct oxygen transfer, and is faster than interconversion of the tri- and tetra-peroxomolybdates. Reaction is probably in the interfacial region surrounding the aqueous microdroplet. Direct oxygen transfer is very slow in anionic water-in-oil (w/o) microemulsions of AOT in hexane, or sodium dodecylsulfate (SDS) and n-butyl alcohol (n-BuOH) in CHCl3. There is oxidation involving singlet oxygen which escapes into the organic solvent and is trapped by PhSMe. This reaction is slower than the direct oxygen transfer from Mo(O2)42− in the cationic microemulsion.