A good understanding of the fundamental transport phenomena of water and methanol in PSA (Perfluoro Sulfonic Acid) membranes is one of the keys in developing efficient direct methanol fuel cells (DMFCs). Electro-osmosis, being one of the most important water and methanol transport mechanisms in DMFCs, has been investigated with a number of different proton exchange membranes. Two aspects were of particular interest: firstly, the interdependencies between the electro-osmotic drag coefficient and methanol concentration and temperature, and secondly the interdependence between the electro-osmotic drag coefficient and current density. The results of these investigations are compared to published data.