two-phase oil/water system was measured using a total internal reflectance static transfer cell. A two-step reaction mechanism between nickel(II) and HNAPO was found to satisfactorily explain the observed initial reaction rate (R-int). The addition of neutral surfactants, nonionic octaethylene glycol mono-n-dodecyl ether and zwitterionic n-dodecyidimethyl-3-ammonio-1-propanesulfonate, decreased R-int, which could be accounted for with a competitive surface adsorption model. The presence of the anionic surfactant sodium dodecyl sulfate accelerated and then decelerated R-int, while the cationic surfactant dodecyltrimethylammonium chloride caused a decrease. The effects of these charged surfactants were accounted for using a combination of a competitive surface adsorption model and the Boltzmann distribution of charged species.