Method of treating a portion of subterranean formation, comprising providing a water in oil emulsion of a water-soluble polymer, said emulsion comprising at least an inverting agent, and at least an emulsifying agent, wherein the mass ratio R of the total amount of inverting agent to the total amount of emulsifying agent is superior to 1.2, wherein the water in oil emulsion contains from 0.5% to 6% by weight of inverting agent; inverting the water in oil emulsion by adding it into an aqueous fluid to form an injection fluid; introducing the injection fluid into portion of the subterranean formation.