A fluid-loss pill that includes a brine solution and an effective amount of a viscoelastic surfactant is disclosed. The viscoelastic surfactant preferably includes at least one compound selected from the family of compounds described by where R1, R2, R3, R4 and R5 are carbon atom or carbon chains, saturated or unsaturated, single or multiple unsaturation, straight chain, branched chain or cyclic including aromatic or alicyclic groups, and R1 contains 16–26 carbon atoms, R2 contains 2–10 carbon atoms, R3, R4 and R5 contains 1–6 carbon atoms. Methods of treating a well that include injecting fluid-loss pill into a well to control lost-circulation or to kill a well.