The influence of the product on the kinetics of the MTBE synthesis reaction has been investigated. Experimental reaction rates for the MTBE synthesis reaction in the liquid phase by addition of methanol (MeOH) to isobutene (IB) were determined on the sulfonic macroporous resin Bayer K2631 at 45-90 degreesC for a wide range of IB, MeOH, and MTBE concentrations and operating in the differential regime in a tubular reactor system. The affinity between the bulk phase and the resin depends on the composition of the reaction medium, and it plays an important role in the catalyst activity. This effect has been implemented into the kinetic equation as a function of the resin and the medium solubility parameters. Experimental data are well described through a LHHW mechanism, the surface reaction being the limiting step. The obtained kinetic equation correctly predicted the additional experimental data obtained in a batch reactor. The apparent activation energy was estimated to be 84.31 +/- 1.09 kJ/mol, and the resin solubility parameter was estimated as 23.79 +/- 0.83 MPa1/2 at 25 degreesC.