An aqueous, viscoelastic fluid gelled with a viscoelastic surfactant (VES) is stabilized with an effective amount of an alkaline earth metal oxide alkaline 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, and may also help control fluid loss. When the particle size of the magnesium oxide or other particulate agent is a nanometer scale, for instance having a mean particle size of 100 nm or less, that scale may provide particle charges that use chemisorption, “crosslinking” and/or other chemistries to associate and stabilize the VES fluids, and also help trap or fixate formation fines when deposited into a proppant pack in a fracture.