A simple method for analyzing the thermal chemical vapor deposition rate using a thin tubular reactor under isothermal and nonisothermal conditions was demonstrated. The inner diameter of the reactor tube was varied from 1.6 to 10.2 mm. The thin tube reduced the mass transfer resistance and kept the gas composition practically constant. Since the gas composition was known, it was possible to simultaneously obtain the growth rate data at different temperatures in the nonisothermal reactor. The mass transfer resistance was examined by measuring the effect of total pressure on the deposition rate. By varying the tube diameter, and hence the volume-to-surface ratio, it was judged that the dominant reaction path of the carbon deposition from ethylene was the surface reaction. A determined Langmuir-type growth rate equation represented well the experimental rates. (c) 2005 Elsevier B.V. All rights reserved.