Naphtha cracker feedstocks contain 10–25 wt% aromatic hydrocarbons, which are not converted into the desired products ethylene and propylene. The conventional processes for the separation of aromatic and aliphatic hydrocarbons are extraction, extractive distillation and azeotropic distillation. These processes are highly complex and demand a high energy consumption. Therefore, alternative separation processes are of interest, such as pervaporation (PV) and vapour permeation (VP) with zeolite membranes. For a feasible process, the purity of both the aromatic and aliphatic products must be 98 wt%. In order to obtain these purities with PV or VP, using a reasonably sized membrane area, the selectivity must be high, at least 40, and preferably above 80, and the flux rate (100 wt% benzene) has to be in the order of 8 kg/m2.h (presently around 0.3 kg/m2.h). For a feed stream of 300 t/h, containing 10 wt% aromatics, a membrane area of more than 60,000 m2 is required with these selectivities and flux rates. The conclusion is that with the current high price level of zeolite membrane modules, around unkeyable??? 2,000/m2, the investments become uneconomical. Therefore, the membrane costs must be reduced, to about unkeyable??? 200/m2.