The reactions of soot particulates and carbons with three oxidising agents expected in the exhaust gases from a diesel engine have been studied. Nitrogen dioxide has been found to be an efficient gasifying agent for carbons, carbon oxides and nitric oxide being produced. The reaction with diesel particulates commences above c. 150 degrees C : with graphite, gasification became significant only above c. 550 degrees C. The presence of oil on the particulates does not affect gasification.