Water-in-oil emulsions of monomers which form water-soluble polymers are polymerized in the presence of a biphase initiator system containing both an oil-soluble initiator and a water-soluble initiator or activator or alternatively a water-soluble initiator and an oil-soluble activator which results in polymers having improved performance characteristics. In addition, the system permits the satisfactory polymerization of monomers which could not have been reproducibly polymerized.