A method of significantly improving carbon nanotube or carbon nanofiber yield from catalytic chemical vapor deposition of a carbon-containing gas comprising at least one hydrocarbon with the assistance of a proper amount of carbon dioxide (CO2). The catalytic particles preferably contain at least one metal from Group VIII (Fe, Co, Ni or the like) or / and one metal from Group VIb, including Mo, W, and Cr. The catalytic particles are preferably supported on oxide powders such as MgO, Al2O3, SiO, CaO, TiO, and ZrO, or a flat substrate such as, but not limited to, a Si wafer. The carbon nanotube or nanofiber product is preferably formed by exposing the catalyst to a mixture of a carbon-containing gas comprising at least one hydrocarbon with a proper amount of CO2 at a sufficiently high temperature. In an alternative embodiment, other oxygen-containing gases, such as alcohols, may be included in the mixture in addition to carbon dioxide.