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The macroviscosity of a single-phase toluene/styrene/sodium bis(2-ethy1hexyl)sulfosuccinate/water/acrylamide Winsor IV inverse microemulsion prior to polymerization as a function of the volume fraction QaW, of the dispersed aqueous (water + acrylamide) phase at 20°C reaches three distinct maxima of 16, 66, and 30 mPa*s for @aw values 25%, 46%, and 62%, respectively. At 60°C, the viscosity maxima practically vanish and the macroviscosity of the dispersion systems is in the range of 5-7 mPa-s. The overall maximum (co)polymerization rate of acrylamide and styrene increases with increasing @aw. On the other hand, an increase of the mass ratio styrene/toluene leads (for a given eaW value) to a decrease of the overall maximum (co)polymerization rate regardless of the nature of the initiator used. This points to an effective competition between monomer in the oil phase (slow homopolymerization of styrene and/or (co)polymerization of styrene with acrylamide dissolved in the oil phase) and monomer in the water pools of inverse micelles (rapid homopolymerization of a major part of acrylamide) for initiator radicals and/or (co)oligomer radicals.