Diffuse-reflectance FTIR results obtained with tert-amyl-methyl-ether (TAME), ethanol, methanol, i-amylenes and mixtures of i-amylenes with alcohols supported a Langmuir-Hinshelwood type reaction mechanism involving adsorbed i-amylene molecules, which form a bridged structure between the adsorbed alcohols and the -SO3H sites of Amberlyst-15. Number of available sites involved in the adsorption of i-olefins is drastically decreased with an increase in alcohol concentration. The reaction rate model, which was proposed basing on the DRIFTS results, was shown to give good agreement with the published initial rate data for TAEE synthesis. The rate of tert-amyl-ethyl-ether (TAEE) formation was found to give a rather sharp maximum at an ethanol activity smaller than 0.1. (c) 2004 Elsevier B.V. All rights reserved.