The synthesis of multiwalled carbon nanotubes (MWCNTs) and carbon balls (CBs) catalyzed by ferrocene (Fc), Mo(CO)5L (L = CO, tBuNC), and bimetallic catalyst systems (Fc/M(CO)5tBuNC; M = W or Mo) was investigated. These reactions were carried out in flowing 5% H2 in Ar in the temperature range 700−900 °C. Under the reaction conditions, Fc yielded CNTs and CBs, while the M(CO)5L complexes yielded little carbonaceous material. Depending on the temperature and weight ratio of the metals used, mixtures of Fc and M(CO)5L generated varying amounts of CNTs and CBs. EDS and TEM analysis revealed the formation of large particles of Mo/Fe alloys. It was observed that the diameters of the CNTs catalyzed by Fc are smaller while the diameters of CBs are larger relative to the diameters of CNTs and CBs produced by the bimetallic catalyst systems. In all instances MWCNTs were produced, which contrasts with the single-walled CNTs produced by Fe/Mo-supported heterogeneous catalyst systems.