The liquid phase alkylation of toluene with 1-heptene was investigated over a HFAU zeolite (Si/Al=6) under the following conditions: batch reactor, 90 degrees C, molar toluene/heptene ratio=3. Monoheptyltoluenes are rapidly formed, whereas biheptyltoluenes appear in low amount at high conversion. A large amount of mono, bi and triheptyltoluenes is shown to be trapped in the zeolite pores, suggesting that alkylation is limited by product desorption. After total consumption of heptene, there is an increase with reaction time in monoheptyltoluenes trapped in the pores and a decrease in bi and triheptyltoluenes. These observations can be explained both by a transalkylation reaction between bi and triheptyltoluenes trapped in the zeolite micropores and toluene molecules and by a slow diffusion of monoheptyltoluenes from the liquid phase to the zeolite micropores.