AbstractA study has been made of the reactions of benzene in a continuous‐flow microwave‐discharge reactor. The distribution of reaction products was found to depend on the reactor pressure and flow‐rate. By accounting for all reaction products (solid, liquid and gas) an overall mass balance was obtained. The reactions are not the result of simple pyrolysis.The insertion of nickel wire into the reactor enhanced the reactions which proceed via a radical—radical mechanism. The addition of carbon dioxide to the benzene feed appeared to retard reactions which involve highly energetic ionisation processes. Thus, the presence of carbon dioxide changed the reaction selectivity. The carbon dioxide did not react chemically.Comparison with other work with benzene shows that the behaviour of this reactor system is significantly different from the behaviour of reactors which operate at a lower frequency. It is suggested that the distribution of electron energies in the microwave discharge is narrower than the energy distributions which are encountered in lower‐frequency and d.c. discharges.