A cross-linking composition comprising (a) an aqueous liquid; (b) a pH buffer; (c) a cross-linkable organic polymer; and (d) a solution of a zirconium cross-linking agent comprising the product of contacting a zirconium complex with an alkanolamine and ethylene glycol wherein the mole ratio of alkanolamine to zirconium is 2:1 to 4:1 and the mole ratio of ethylene glycol to zirconium is 1:1 to 10:1. Optionally, water, hydroxyalkylated ethylenediamine, or both are added to the zirconium complex. The cross-linking composition of this invention is useful in oil field applications, for example, for hydraulically fracturing a subterranean formation and for plugging permeable zones or leaks in a subterranean formation.