The chemical kinetics of the pyrolysis of the hydrocarbons ethylene, acetylene, and propylene are modeled in detail under conditions relevant to the chemical vapor deposition of pyrolytic carbon. A mechanism that consisted of 227 species and 827 reactions (most of which are reversible) is developed and computed using a software package designed for computing time-dependent homogeneous reaction systems. Experimental results used for model validation are obtained using a vertical flow reactor at 900 degrees C, pressures of 2-15 kPa, and residence times of up to 1.6 s. The products are analyzed using on-line and off-line gas chromatography. Computational and experimental results are compared for more than 30 products, including hydrogen, small hydrocarbons (ranging from methane to C-4 species), and aromatic hydrocarbons (ranging from benzene to coronene). The resulting reaction model predicts the profiles of the major pyrolysis products (mole fractions of > 10(-2)) of the three hydrocarbons, as a function of both residence time and pressure, with satisfactory accuracy. It also predicts the mole-fraction profiles of minor compounds, ranging from polycyclic aromatic hydrocarbons (PAHs) to naphthalene, fairly well; however, it significantly underpredicts the larger PAHs. The deviation increases as the molecular mass of the PAHs increases. Sensitivity and reaction-rate analyses were also conducted to identify crucial reaction steps.