Fuel composition can have a significant effect on soot formation during gas turbine combustion. Consequently, this paper contains a comprehensive review of the relationship between fuel hydrocarbon composition and soot formation in gas turbine combustors. Two levels of correlation are identified. First, lumped fuel composition parameters such as hydrogen content and smoke point, which are conventionally used to represent fuel sooting tendency, are correlated with soot formation in practical combustors. Second, detailed fuel hydrocarbon composition is correlated with these lumped parameters. The two-level correlation makes it possible to predict soot formation in practical combustors from basic fuel composition data. Threshold sooting index (TSI), which correlates linearly with the ratio of fuel molecular weight and smoke point in a diffusion flame, is proposed as a new lumped parameter for sooting tendency correlation. It is found that the TSI model correlates excellently with hydrocarbon compositions over a wide range of fuel samples. Also, in predicting soot formation in actual combustors, the TSI model produces the best results overall in comparison with other previously reported correlating parameters, including hydrogen content, smoke point, and composite predictors containing more than one parameter. (c) 2006 The Combustion Institute. Published by Elsevier Inc. All rights reserved.