An aqueous, viscoelastic fluid gelled with a viscoelastic surfactant (VES) is stabilized and improved with an effective amount of an alkali earth metal oxide alkali earth metal hydroxide, alkali metal oxides, alkali metal hydroxides transition metal oxides, transition metal hydroxides, post-transition metal oxides, and post-transition metal hydroxides. These fluids are more stable and have a reduced or no tendency to precipitate, particularly at elevated temperatures. The additives may reduce the amount of VES required to maintain a given viscosity. These stabilized, enhanced, aqueous viscoelastic fluids may be used as treatment fluids for subterranean hydrocarbon formations, such as in hydraulic fracturing. The particle size of the magnesium oxide or other agent may be nanometer scale, which scale may provide unique particle charges that use chemisorption, crosslinking and/or other chemistries to associate and stabilize the VES fluids.