The paper describes the pyrolysis of fossil fuels and model nitrogen compounds in helium in a small quartz plow reactor, as part of a study of the chemical mechanisms involved in the conversion of fuel-nitrogen compounds to nitric oxide (NO) during combustion. Hydrogen cyanide (HCN) was the major nitrogen-containing product obtained in all cases, indicating that HCN is formed during the initial pre-flame stages of combustion and is the principal intermediate in the formation of fuel NO. At a nominal residence time of 1 second, 50% decomposition of pyrrole, quinoline, benzonitrile, and pyridine occurs at 905, 910, 922, and 954 C, respectively. The fraction of the nitrogen in pyridine that is converted to HCN increases from 40% at 960 C to 100% at 1100 C. Benzonitrile produces similar amounts of HCN (49 and 82%). The HCN yields from coals and residual fuel oils increase from the range of 15-25% at 950 C to 23-42% at 1100 C. It is not possible to determine from these single-stage experiments if most of the HCN forms in the primary pyrolysis process or in secondary reactions.