A refinery with a solid phosphoric acid olefin oligomerization unit can reduce the benzene content of its motor-gasoline by co-feeding the benzene-containing material to that unit. It has been shown that benzene co-feeding has little disruptive impact on olefin oligomerization, and > 80% benzene conversion to alkylated benzenes has been demonstrated during a commercial test run on an industrial unit. Benzene conversion is insensitive to reactor inlet temperature in the range of 160-180 degrees C and remains better than 80% at liquid hourly space velocities of up to 1.5 h(-1). A high propene content in the olefinic feed promotes benzene alkylation, and although butene-rich feeds can be employed, benzene conversion is lower.