The invention discloses a method of treating a wellbore by providing an aqueous mixture of a hydrated polysaccharide with a salt; adding to the mixture a cross-linking agent for cross-linking the hydrated polysaccharide, wherein the cross-linking agent comprises a zirconium compound, glutamic acid, and a polyol; pumping the aqueous mixture of the hydrated polysaccharide and the cross-linking agent into the wellbore; and cross-linking the hydrated polysaccharide.