Short contact time monolithic reactors have been examined for the production of ethylene by oxidative dehydrogenation over a supported Pt catalyst. The results so far suggest that these reactors may revolutionize the way chemical synthesis is conducted, but many questions remain. This paper addresses the co-production of acetylene. Under some conditions, acetylene is produced as a byproduct during the oxidative dehydrogenation of ethane. This acetylene formation appears to be due to homogeneous reactions since the acetylene production increases at higher reaction temperatures and under conditions where there is little available surface area for radical quenching.