Y-junction carbon nanotubes can be produced in relatively large quantities by the vapor phase pyrolysis of a mixture of cobaltocene or ferrocene with thiophene in a hydrogen atmosphere. Pyrolysis of Ni- and Fe-phthalocyanines or Fe(CO)(5) with thiophene also yields Y-junction nanotubes. Good yields of Y-junction nanotubes were obtained by pyrolyzing thiophene over an Ni(Fe)/SiO2 catalyst as well. Many of the nanotubes show multiple Y-junctions. Of the various methods employed by us, the pyrolysis of thiophene with metallocenes or over a Ni(Fe)/SiO2 catalyst yields the best results and the latter is a less expensive route. The availability of large quantities of Y-junctions by the procedures employed here should render them useful for exploitation in nanoelectronics.