Electro-osmotic drag coefficients for Nafion 117, polystyrene sulfonic acid (CR61 CMP), and polybenzimidazole were investigated in the presence of phosphoric, sulfuric, and hydrochloric acid. The coefficients vary with acid concentration and type with polymer structure and with water content, as illustrated by conductivity, transference number, and partition coefficient measurements. The results have implications for fuel cell performance and in the development of new polymer electrolyte membranes. (C) 2004 The Electrochemical Society.