Methanol-ethanol mixtures enable simultaneous quantification of bimolecular dehydration turnover rates (373 K, per H+) to dimethyl ether (DME) and methyl ethyl ether (MEE) on chabazite zeolites. Coverage terms for protonated alkanol clusters rigorously cancel in DME and MEE formation rate expressions, and enables isolating the kinetic relevance of trimer-mediated pathways to form DME, but not MEE, at high coverage (373 K, 2-50 kPa CH3OH). The kinetics of parallel product formation provide experimental evidence that DME formation rates are inhibited when larger protonated CH3OH clusters form (>3 CH3OH/Fr) because they must desorb CH3OH to form kinetically-preferred trimer-mediated transition states. (C) 2020 Elsevier Inc. All rights reserved.