Based on a comparison between simulated and measured adsorption properties, we demonstrate that both normal and monomethylparaffins are able to fully enter the pores of TON-, MTT-, and AEL-type molecular sieves. This disproves the theory that monomethylparaffins only partially enter these pores and that normal paraffins are predominantly hydroisomerized at the pore mouths of these sieves. Instead, we attribute the high selectivity for paraffins with terminal methyl groups to product shape selectivity, and the low selectivity for paraffins with neighboring methyl groups to transition state selectivity. These traditional shape selectivity concepts explain not only the detailed product distribution of n-heptane hydroconversion, but also that of longer-chain n-paraffins.