In oxygen enriched methane diffusion flames. carbon nanotubes were discovered to be formed in the region on the fuel-rich side of the flame front at an oxygen enrichment of 50%. No catalyst was employed. An opposed flow diffusion flames with varying strain rate and oxygen content in the oxidizer stream was used. Substantial quantities of nanotube material are produced at atmospheric pressure in this continuous (non-batch) process. Thermophoretic sampling of the flame and collecting the carbon material deposited near the exhaust was done. Both confirm the growth of carbon nanotubes and other carbon clusters. (C) 2002 Elsevier Science B.V. All rights reserved.