Mechanism and kinetics of gasphase synthesis of ethyl-tert-butyl ether (ETBE) over Wells-Dawson heteropolyacid H6P2W18O62 in an anhydrous system have been discussed. The rates of ETBE synthesis were measured in a differential reactor for ethanol-isobutene system, far from the limitation by chemical equilibrium. In the pressure range studied, kinetic measurements show that isobutene has an enhancing effect on the reaction while ethanol has an inhibitory one. Catalytic and sorption experiments allowed to formulate the mechanism of ETBE synthesis which assumed isobutene adsorption and oligomerization at the surface of heteropolyacid crystallites and the formation of carbocation using protons supplied from the bulk of catalyst. Kinetic equations were deduced indicating that it is the concentration of protons forming inter-anionic bonds between heteropolyacid anions which determines the catalytic activity of heteropolyacid. (c) 2006 Elsevier B.V. All rights reserved.