The viscous flow properties of polymer-thickened water-in-oil emulsions were measured using a coaxial cylinder viscometer. The emulsions were prepared using deionized water and polyisobutylene in oil solutions. Three different molecular weight polyisobutylenes (Vistanex MML-140, Vistanex MML-100, and Vistanex MML-80) were studied. The effects of polymer concentration and water (droplet) concentration on the flow properties were determined. The polymer concentration varied from 0 to 3.96% by weight based on the oil phase whereas the water concentration varied from 0 to 80% by volume (based on total emulsion volume). The polymer solutions behaved like non-Newtonian Ellis model fluids. At low water concentrations, the flow curves for emulsions were similar to their suspending medium (polymer solution). At high values of water concentration, emulsions clearly exhibited a yield stress. The yield stress increased with both water and polymer concentrations. The shear stress/shear rate data for the emulsions possessing a yield stress were described adequately by a modified Herschel-Bulkley model. A comparison was also made of the relative viscosities of emulsions having different polymer concentrations. The relative vis-cosities for polymer-thickened emulsions were found to be significantly lower than the corresponding values for emulsions without polymer. The correlation of relative viscosity/ concentration data is discussed. © 1993 John Wiley & Sons, Inc.