Experimental results are described which identify the dependence of soot production on fuel molecular structure in strongly backmixed combustion. This type of aerodynamic process simulates that occurring within the primary zone of many continuous combustion devices (e.g. the gas turbine) where fuel-air ratio conditions are sufficiently rich to form appreciable quantities of soot. Results to be presented are gaseous combustion product distributions, incipient soot limits, and soot production. These parameters have been developed for a variety of hydrocarbons which represent constituents of practical fuels—normal and cyclic paraffins, olefins, single-ring aromatics, and double-ring aromatics. Substantial differences in sooting behavior between the aromatic and aliphatic hydrocarbons have been found and important observations regarding the presence of unburned hydrocarbons at and near the soot limit have been made.