A process for the production of high octane number gasoline from light refinery olefins and benzene-containing aromatic streams such as reformate. The process achieves good utilization of both the ethylene and the propylene present in the mixed olefin feed from the unsaturated gas plant while reducing gasoline benzene levels. The light olefins including ethylene and propylene are reacted with the light aromatic stream containing benzene and other single ring aromatic compounds to form a gasoline boiling range product containing akylaromatics. The reaction is carried out with a two-catalyst system which comprises a member of the MWW family of zeolites and an intermediate pore size zeolite such as ZSM-5 using a fixed catalyst bed in both stages. Use of the two catalyst system enables the conversion of the ethylene and propylene components of the olefin feed to be converted to alkylaromatics under favorable conditions.