A T-63 combustor rig has been used to study the sensitivity of combustor performance to the physical and chemical properties of fuels. The purpose was to determine the impact of broadening fuel specifications and using non-specification fuels in emergencies. The fuel properties of special concern were the composition, the distillation curve and viscosity. The first property is associated with the chemistry of carbon formation while the latter two are related to mixing as they affect the atomization and vaporization. Six fuels were blended from a JP-5 base fuel and used to determine the effects of aromatic content, types of aromatics, and end point. Three JP-5s derived from coal, shale oil, and tar sands, were used to see if they correlated the same as the petroleum-derived fuels despite their different chemistry. Seven more fuels that were blends of marine diesel, JP5, and gasoline were used to examine all aspects but with emphasis on viscosity and distillation curve. Four emulsified fuels containing 5, 10, 20 and 30% water were prepared with one of the above high aromatic JP-5 fuel blends. Two more emulsified fuels containing 10 and 20% water were prepared with the shale oil derived JP-5.The combustor was instrumented for flame radiation, exhaust smoke, and gaseous emissions. Measurements of these items were made at the full power condition.The hydrogen/carbon ratio was the most effective correlating parameter for radiation and smoke; sensitivities to molecular structure appeared to be secondary. Similar to the syncrude fuels, the water/fuel emissions and methanol/aromatic blends correlated in the same way as petroleum fuels. Higher end points did not affect the correlation indicating that soot formation was due to gas phase reactions not liquid phase pyrolysis. The results favor a chemical mechanism for the role of water in reducing soot.