The initial pathways of JP-10 (exo-tetrahydrodicyclopentadiene) decomposition are expected to have a significant effect on combustion and pyrolysis behavior of the fuel, affecting, for example, product distribution and ignition delay. Modeling of JP-10 decomposition should capture these initial decomposition processes as accurately as possible. Two classes of computational approaches have been applied to study intramolecular disproportionation—an important class of reactions in the initial stages of JP-10 decomposition: (1) the second-order, multiconfigurational, quasidegenerate perturbation theory employing the complete active space self-consistent field (CASSCF) reference; and (2) the size-extensive, left-eigenstate, completely renormalized (CR) coupled-cluster (CC) method with singles, doubles, and noniterative triples, termed CR-CC(2,3), capable of describing reaction pathways involving biradicals. Applying higher levels of theory to points along the CASSCF reaction paths, the barriers to intramolecular disproportionation are much smaller and some barriers appear to vanish. The conventional ring-opening + disproportionation pathway is compared with an alternative concerted reaction pathway. Overall, this investigation has yielded insights into alkyl disproportionation and ring-opening reactions that may be of more general use in chemical kinetic modeling. © 2012 Wiley Periodicals, Inc. Int J Chem Kinet 44: 179–193, 2012