Desulfurization of commercial gasoline and diesel by a pi-complexation adsorbent, Cu(I)-Y zeolite, was studied in a fixed-bed adsorber operated at ambient temperature and pressure. The sulfur contents in the effluents were below (or well below) the detection limit using flame photometric detection (FPD), i.e., below 0.28 ppmw sulfur. Thus, these "sulfur-free" fuels are well suited for fuel cell applications. Furthermore, it is demonstrated that using a thin layer of a guard bed (e.g., activated carbon, AC) could significantly increase the sulfur capacities of the pi-complexation sorbent. For a feed gasoline containing 335 ppmw sulfur, Cu(I)-Y produced 14.7 cm(3) of sulfur-free gasoline/g of sorbent. When using AC as a guard bed, 19.6 cm(3) of sulfur-free gasoline/g of combined sorbent was produced. For the case of diesel fuel, 34.3 cm(3) of "sulfur-free" diesel was produced per 1 g of combined sorbent. The pi-complexation sorbents have proven to be by far the most sulfur-selective as well as having the highest sulfur capacities. Gas chromatography-FPD results showed that the pi-complexation sorbents selectively adsorbed highly substituted thiophenes, benzothiophenes, and dibenzothiophenes from gasoline and diesel, which is not possible by using conventional hydrodesulfurization reactors.