Trace amounts of ethylene impurities in the methane used for benzene methylation over ZSM-5 and H-beta catalysts are found to enhance benzene conversions and selectivity to ethylbenzene. However, methane containing ethane impurities yielded negligible benzene conversion in the absence of oxygen over CoZSM-5 while a much higher conversion is obtained over H-beta due to cracking of benzene as previously reported.