A viscoelastic gelled oil, for example gelled diesel or paraffin oil, is made with a gelling agent, for example a phosphate ester, a metal carboxylate, for example an aluminum carboxylate, and a gel-enhancing surfactant, for example a zwitterionic surfactant, for example erucylamidopropyl betaine. The gel-enhancing surfactant makes the gel viscoelastic, increases the stability and decreases the sensitivity to the concentrations of the gelling agent and the metal carboxylate. The enhanced viscoelastic gelled oils are used, as examples, in hydraulic fracturing, frac packing, gravel packing, diversion, fluid loss control, lost circulation control, sand control, wellbore cleanout, wellbore or pipeline sweeping, organic scale dissolution, organic scale removal, and drilling.