This study is a continuing effort toward the goal of understanding deposit formation process in a combustion chamber by probing the impacts of engine operating conditions and fuel compositions on the formation of combustion chamber deposits.To facilitate the study, four retrievable deposit sampling probes were used. The engine operating parameters investigated include coolant temperature, spark advance, manifold air pressure (engine load), and fuel-air ratio. As a continuum of previous studies, toluene was used as the base fuel. In addition, CCD-forming tendencies of isooctane and other aromatics with higher boiling points were investigated.Coolant temperature, fuel-air ratio, and boiling point of the fuel have significant impacts on both the amount and the morphology of deposits formed in a combustion chamber. In contrast, spark advance has little impact on either deposit weight or deposit morphology. Manifold pressure has an intermediate impact on CCD. The surface temperature can only partially explain the experimental results. There is strong evidence that deposit precursors are partially reacted fuel in the gas phase.