The primary objective of this work is to develop an improved fundamentally-based mechanism that describes the molecular weight growth kinetics observed during propene pyrolysis. Earlier attempts to describe the kinetics in terms of theoretically plausible reactions generally under-predicted the low temperature reactivity. To address this issue, propene pyrolysis experiments were performed at 575-875 degrees C with nominal residence times of similar to 2.4, 1.2 and 0.5 s at similar to 0.83 atm. These data were compared to a kinetic model that includes several reactions that involve allyl radicals. Specifically, electronic structure calculations at the CBS-QB3 level were performed for various allyl radical reactions, including addition, recombination, and hydrogen abstraction. This updated model is able to capture the observed fuel conversion, production of major products, and formation of molecular weight growth species. The sensitivity and rate of production analyses show that allyl reactions play important roles for both fuel conversion and product formation. In particular, allyl addition to propene leads to production of CH3 and H. The H-atoms can add to propene to form CH3 radicals, and both CH3 and H can abstract from propene to regenerate allyl, completing the reaction chain. This model also successfully predicts the fuel conversion and major products for selected literature propene pyrolysis data. (C) 2015 The Combustion Institute. Published by Elsevier Inc. All rights reserved.