The kinetics for the liquid phase synthesis of methyl tert-butyl ether (MTBE) from isobutene and methanol using Amberlyst 18 (A18) ion exchange resin as catalyst was experimentally determined in a batch reactor in the temperature range 323–338 K and pressure range 0.8–1.0 MPa. Only methanol and MTBE are sorbed on the active acid sites. The reversible surface reaction on the pore walls and within the gel phase of the microparticles is the rate controlling step; the forward reaction is first order in isobutene and sorbed methanol and the reverse reaction is first order in sorbed MTBE. The experimental results can be described by a two parameter model based on a Rideal-Eley rate expression in liquid phase concentrations; the parameters are the forward reaction rate constant, kar, and the ratio between adsorption/desorption equilibrium constants of MTBE and methanol, D. The reactor model involved mass balances in both the gas and bulk liquid as well as in the macropores and microparticles and also energy balances in the catalyst particle and liquid phase. The activation energy was determined to be 130.2 kJ/mol.