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Six chemically defined fuels have been run in a 2.0 liter production engine, in both a deposit-free and deposited state, at five different operating (speed/load) conditions. The fuel used to produce the deposits minimized the development of deposits in the intake system, so that primarily the effect of combustion chamber deposits were considered in this study. The six chemically defined fuels investigated were based on an iso-octane and toluene mix (base fuel). Methyl tertiary butyl ether, cyclohexane, diisobutylene, 1,2,4 trimethylbenzene and ethylbenzene were added to this base fuel to form five tertiary fuel mixtures. Engine-out emissions of speciated hydrocarbons, NOx, CO and CO2 were measured for the base fuel and five tertiary fuel mixtures in both the deposit-free and deposited state. NOx emissions were seen to increase relative to the base fuel for the cyclohexane and ethylbenzene tertiary fuel mixtures.