The scale-up of stirred tank contactors on the drop size of emulsion-solvent dispersion and the mass transfer coefficient of hydrocarbon in oil-in-water O/W emulsions (dispersed phase) are discussed. Correlative equations to estimate the drop sizes and the mass transfer coefficient are proposed without regard to tank size and material systems. The consumption of power created by stirring one unit of liquid tank volume is an applicable scale-up standard for the drop size of O/W emulsion and the mass transfer coefficient of hydrocarbons in the emulsion.