Single- and double-walled carbon nanotubes were produced in high yield using the selective reduction of solid solutions of Mg1-xCoxO in a methane and hydrogen atmosphere at 1000degreesC. The solid solutions were prepared using combustion synthesis with urea as the fuel. The BET surface areas ranged from 10 to 65 m(2)/g depending on the fuel content. A single crystalline phase was obtained only for fuel-rich compositions. Increased fuel content increased the surface area by a factor of 6. However, very high fuel contents (> 4 times the stoichiometric amount) caused a demixed solid solution. Surface-area measurements and Raman spectra showed that the quantity of nanotubes formed depended on the surface area and composition of the precursor oxide.