A method for the in situ synthesis of multi-walled carbon nanotubes in a bulk solid composition from the pyrolysis of a mixture formulated from Co-2(CO)(8) and various high temperature phthalonitrile resins is presented. Carbon nanotube containing compositions in various forms (solid, fiber, and film) can be readily fabricated by this method utilizing slight modifications to the standard resin processing techniques. The formation of carbon nanotubes occurs during the carbonization process at ambient pressure. X-ray diffraction, scanning electron microscopy, and transmission electron microscopy studies show the presence of a copious amount of multi-walled carbon nanotubes in the carbonaceous composition. Published by Elsevier Ltd.