Vanadium pentaoxide nanoparticles can be made by adding vanadyl isopropoxide to water contained in a reverse microemulsion of Aerosol OT in toluene. First-order rate constants of this process are on the order of 40 s(-1), as measured using a stopped flow reactor, These rate constants are directly proportional to the water concentration and inversely related to the surfactant concentration. While this behavior is inconsistent with earlier theories for reactions in dilute detergent solutions, it is consistent with a reaction limited by alkoxide transport across a thick surfactant layer surrounding the micelles’ water core.