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Two V-6 engine types were investigated for the physical mechanisms causing combustion chamber deposit (CCD) formation. Experimental techniques and parameters such as combustion chamber deposit weights, thicknesses, thermogravimetric analysis (TGA), inductively coupled plasma (ICP) and solid state 13C nuclear magnetic resonance (NMR) were used to determine both the chemical and physical characteristics of combustion chamber deposit material. An analysis of the results indicated a mechanism for combustion chamber deposit formation consistent with that originally developed by Lepperhoff.1 Lepperhoff proposed that four layers exist in the combustion chamber deposit morphology. In contrast, the investigation described below has led to identification of only two distinct CCD morphologies.