Organized carbon nanotubes (CNTs) have been grown at a fast rate by a pentacarbonyl-catalyzed chemical-vapor-deposition technique with acetylene as the carbon source at 600-750 degrees C for 15 min. Multiwall CNTs were obtained. Organized CNTs facilitate the quantitative analysis of growth kinetics. The CNT growth increased with growth temperature up to 700 degrees C, but depended upon the amount of acetylene at 750 degrees C. High acetylene input poisoned catalysts and led to the difficulty in CNT growth. Hydrogen rejuvenated the poisoned catalysts for enhancing CNT growth at higher temperatures via a hydrocarbon reaction. Organized CNTs with a tube length above 600 mu m were obtained in 15 min. A kinetic model based upon the carbon flux is proposed to explain the CNT growth of our complex deposition system. The carbon flux is mainly proportional to the concentration of dissolved carbon and to the carbon concentration difference between the dissolved carbon and the Fe3C solution. This kinetic model can be successfully applied to qualitatively demonstrate the effects of process parameters on our CNT growth.