Carbon samples are being investigated with thermogravimetry, infrared spectroscopy and transmission electron microscopy. We focus on a spark discharge Soot, soot from a heavy-duty diesel engine, soot from a diesel engine in black smoking conditions and a furnace carbon black from Degussa. The aim of this study is to correlate reactivity towards oxygen, functional groups and nanostructure. It is found that the amount of defects as well as the functionalisation plays an important role in the onset of combustion in the thermogravimetric experiments. Clear differences in reactivity towards oxidation are observed. (c) 2005 Elsevier B.V. All rights reserved.