The applicability of four catalyst with different composition (conventional and new generation CoMo/ Al 2 O 3 , new composition Pt,Pd/USY, Pt/H-Mordenite) catalysts was investigated for selective desulphurization of different sulphur containing FCC gasolines. The new generation CoMo/Al 2 O 3 and the new composition Pt,Pd/ USY were found to have favourable hydrodesulphurisation activity. The reactions of some C 5 -C 6 olefin and aromatic hydrocarbons are discussed under the conditions of deep desulphurisation, highlighting the effects of that on the octane number.