The effect of operating temperature on permeation flux in pervaporation was analyzed. In the standard pervaporation processes, both the permeability coefficient of a membrane and the driving force for mass transport are influenced by temperature. The so-called "activation energy" of permeation, E(J), conventionally obtained from In J vs. 1/T plot is a compounded parameter characterizing the overall temperature dependence of permeation flux. The activation energy, E(P), characterizing temperature dependence of membrane permeability should be evaluated from the log of driving force-normalized flux vs. 1/T data. When the transmembrane driving force is expressed in terms of partial pressure, E(P) can be evaluated from In (J/Delta p) vs. 1/T plot. A rule of thumb for estimating E(P) is to subtract the molar heat of vaporization from E(J).