Carbon monoxide was used to synthesize carbon nanotubes (CNTs) in a hot-filament chemical vapor deposition (HFCVD) system. Transmission electron microscopic investigation showed that the CNTs were multi-walled and had an average diameter of 30 nm and 20 layers. Nickel was observed in the tips of the nanotubes and played a crucial role in the formation of multi-walled carbon nanotubes (MWNT)s. The CNTs synthesized from carbon monoxide validate the oxide-assisted growth method.