This study presents the results of an experimental study of the effects of water-soluble polymer additives on the dynamic interfacial tension behavior of reacting oil-aqueous systems as measured by the spinning drop tensiometer. Polymer additives can exert both a direct physico-chemical effect and an indirect viscosity effect on the measured interfacial tension. This work, which complements an earlier study dealing with the effects of oil-soluble polymer additives, reveals that the nominal effects of aqueous-phase viscosity are opposite to those of oil-phase viscosity. In particular, an increase in aqueous-phase viscosity produces an increase in the rate of increase of the apparent interfacial tension after attainment of the minimum value. These differences are explained in terms of the dependence of diffusion rates and interfacial adsorption on aqueous-phase viscosity. The conclusion of principal practical interest is that although aqueous-phase viscosity exerts only a small effect on the dynamic interfacial tension at small times (i.e., prior to attainment of the minimum value) it exerts a very significant effect thereafter.