Abstract: Viscoelastic surfactant based aqueous fluid systems are described that are useful in fracturing subterranean formations penetrated by a wellbore. The preferred surfactant compositions contain quaternary ammonium salts wherein the long chain alkyl substituent contains about 3% or less of groups containing 18 or less carbon atoms. The amount of intermediate compounds in the surfactant composition is less than about 1%. The surfactant composition can be used in conjunction with an inorganic water soluble salt such as ammonium chloride or potassium chloride, and an organic stabilizing additive.