AbstractThe influence of unimolecular fall‐off effects on the kinetic modelling of larger pyrolysis systems is estimated theoretically for the case of propane decomposition at nearly industrial conditions (1100 K, 0.1 MPa). The ordinary differential equation system based on a mechanism of 34 elementary reactions and 20 chemical species is integrated by means of a Gear algorithm two times, on the one hand with the thermal high‐pressure rate constants and on the other hand with constants corrected for the fall‐off effects in the case of unimolecular as well as in the case of bimolecular association reactions. RRKM theory, combined with an empirical treatment of weak‐collision effects, provides ratios of k/k∞ between 0.2 and 0.9. It turns out that corrections in this order of magnitude have only little influence on the concentrations of stable products, whereas radical species show, at least partly, a higher sensitivity. This results in larger deviations of the concentrations of compounds formed by radical recombination that, nevertheless, contribute to the overall products only to a small extent.