Simulations of the gas phase chemistry (C(2)H(2)/H(2)) coupled with surface reactions for the catalytic growth of carbon nanostructures (nanotubes/nanofibers), using different activation modes of catalytic chemical vapor deposition (CCVD) process, are presented. Deposits issued from thermal CCVD, hot-filament CCVD, plasma-enhanced CCVD and plasma-enhanced combined with hot-filament CCVD are compared to simulations of the gas phase and surface kinetics. The influence of the activation elements is described in detail. According to these simulations taking into account optical emission spectroscopy data, gas phase composition and linear growth rate of tubular nanostructures are predicted in good agreement with the experimental observations. (C) 2009 Published by Elsevier B.V.