Two critical steps towards soot production in combustors are the decomposition of the fuel and the subsequent formation of aromatic hydrocarbons with one to three benzenoid rings. Traditionally, flame studies of these processes have used small hydrocarbons such as methane, ethylene, and acetylene as the fuel. However, recent research, which is reviewed in this article, has begun to close the 'gap' between these small hydrocarbons and the larger, more complex hydrocarbons that constitute all liquid combustion fuels. (C) 2006 Elsevier Ltd. All rights reserved.