The slow combustion of benzene/phenol gives rise to dibenzofuran (DBF) as major product of incomplete combustion, with negligible proportions of dibenzo-p-dioxin (DBD), or benzofuran (BF). Contrary to a recent proposal that acetylene growth reactions, e.g. BF-->DBF, are important in dioxin formation, co-combustion of benzene/phenol with acetylene--around 550 degrees C--did not alter this product pattern. Also, BF was identified as a product from degradation of DBF.