Many cationic and zwitterionic surfactants are considered excellent drag reducing agents. The properties of two of them, a cationic, CTAC, and a zwitterionic, SPE 98330, are compared in this paper. The hydrodynamic radius of the micelles, the shear and extensional viscosity of the solutions at concentrations appropriate for drag reduction were investigated and the influence of some low concentration salts, which are usually found in tap water, was examined. (C) 2001 Published by Elsevier Science B.V.