Abstract–The formation of carbonaceous deposits in gas turbine combustion chambers has been studied at the Institute for Thermal Turbomachinery at the University of Karlsruhe. The deposits show differing chemical and physical properties over wide ranges. Consequently, different mechanisms of formation are considered. In investigating the dominant parameters for coke deposition the chosen approach was to study the formation process under well defined test conditions. These bench tests were followed by comparison with deposits derived from operating combustors using elementary analysis, gaschromatography, infrared spectroscopy as well as electron microscopy. The development of the deposits by fuel droplet impingement on the hot combustion chamber wall is simulated. In using both gas turbine fuels as well as pure hydrocarbons the influence of wall temperature and fuel composition is examined. As a result of the analysis, a characteristic temperature range for the coke deposition is found. In addition, the deposition-causing fraction of the fuel can be determined. Two different groups of deposits are identified under combustion chamber operation conditions. Deposit formation by droplet impingement accompanied with chemical reactions at the combustor wall is found in the primary zone of the combustor. This is confirmed by identical chemical characteristics between deposits of the bench tests and the combustion chamber deposits. Another typical deposit build-up is formed by adhesion of small particles formed in the reaction zone of the combustor. Based on our results, a scheme for the formation of deposits from the liquid fuel is formulated.