Decomposition of JP-10 (exo-tetrahydrodicyclopentadiene) was studied in a small flowtube reactor over the temperature range up to similar to 1700 K on the millisecond time scale. For comparison, the decomposition behavior of cyclopentadiene, dicyclopentadiene, and benzene was studied under identical conditions. Products of pyrolysis were identified by chemical ionization (CI) and electron impact ionization (EI) mass spectrometry. On the experimental time scale, JP-10 begins to decompose above 900 K and is completely decomposed by 1300 K. In the initial decomposition, the principal products are cyclopentadiene, benzene, propyne, and C4Hx. At high temperatures, the cyclopentadiene decomposes, and the principal species observed are benzene, acetylene, and ethylene. From the combination of EI and CI spectra, we can confirm that the C-6 product observed is benzene, with few if any other C6Hx products. Similarly, the C-5 product is cyclopentadiene, with no cyclopentene or other C5Hx products. The observed product distribution is inconsistent with both equilibrium speciation and predictions of existing JP-10 kinetic models. (c) 2005 The Combustion Institute. Published by Elsevier Inc. All rights reserved.