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The dimerization of isobutene (2-methylpropene) produces diisobutenes (2,4,4-trimethylpentenes) that can be used as high-octane gasoline components. The dimerization kinetics were studied in experiments carried out in a continuous stirred tank reactor at 60−120 °C with different feed concentrations. A commercial ion-exchange resin catalyst was used together with tert-butyl alcohol (2-methyl-2-propanol), which increases the selectivity for diisobutenes by reducing the activity of the sulfonic acid sites of the resin. Langmuir−Hinshelwood-type kinetic models were derived for the dimerization and trimerization reactions, and their parameters were estimated on the basis of the measured data. The only model to represent the data successfully was one where diisobutenes form using two active sites and triisobutenes via diisobutenes using three active sites. This type of model well describes the triisobutene formation rate and the observed maximum in the diisobutene rate. The apparent activation energy was 30 kJ/mol for dimerization.