One of the significant sources of error in the generation of kinetic data, for use in rate expression determination, is the apparatus design. In particular for gas-phase reactions, the design of the quench system is of key importance. The purpose of this paper is to analyze the magnitude of the effect of the quenching system on exit gas product distribution. Two reaction systems, hydrogen sulfide and ethane pyrolysis, were simulated using two different quenching systems (water cooled and air cooled). As expected, the residence time of the quench was found to have an effect on the exit gas distribution, but the temperature profile, which is often ignored, was also found to have a substantial effect. These results highlight the sensitivity of reacting species to the quench and the importance of proper quench design in the design of reactor systems.