<div class="htmlview paragraph">This study investigated the relationship between the average molecular structures of combustion chamber deposits (CCD), the quantity of deposit formed and the aromatic content of the fuel. Solid-state ¹³C nuclear magnetic resonance (NMR) techniques developed for the study of coal were applied to CCDs generated in spark ignition engines on dynamometer test stands. Using these techniques, the molecular structures were identified and related to fuel chemistry, cylinder deposit thickness and cylinder deposit weight. With a better understanding of the structure of the deposits formed during combustion, fuel formulations and CCD control-additive development can be greatly improved.</div>