Introduction Today, almost every gasoline molecule has seen the interior of a zeolite and experienced the effect of shape selectivity. Given the economical importance  implied by this statement, one would expect that we have a very good understanding of the mechanisms underlying shape selectivity. Clearly, we do have a very good understanding of the chemical reactions that take place inside the pores of a zeolite. In addition, many mechanisms have been proposed to explain the various product distributions that have been observed experimentally. However, we are still very far away that by looking at a zeolite structure we can provide a prediction of the products.Let us consider as a simple example the conversion of n-decane in an acid zeolite. The chemistry tells us that isomerization reactions take place giving mono-, di-, and tribranched isomers. These isomerization reactions compete with cracking, and this results in a large number * Corresponding author.