Dilute mixtures of 1,7-octadiene in argon have been decomposed in single-pulse shock tube experiments. The main reaction is the breaking of the carbon-carbon allylic bond leading to the formation of allyl and 4-pentenyl radicals. A minor pathway involving a retroene reaction yielded propene and 1,5-pentadiene. Most of the 4-pentenyl radical decomposes to form another allyl and ethylene. Contributions from a cyclization process resulting in the formation of cyclopentene have also been Allyl radical decomposition rate constants have been measured. The following rate expressions have been determined: k(1,7-octadiene-->allyl+4-pentenyl)=1.2+/-0.8X10(16) exp(-35700+/-400/T)s-1, k(1,7-octadiene-->propene+1,4-pentadiene) =(3+/-1.5)X10(12) exp(-27900+/-250/T)s-1, k(4-pentenyl-->cyclopentene+H)/k(4-pentenyl-->allyl+ethylene)=(6.9 +/-4)X10(-3) exp(2118+/-500/T), and k(allyl-->allene+H)=40+/-10 s-1 at 1080 K. When compared with lower temperature literature data on hydrogen addition to allene to form allyl, the present results are consistent with a resonance energy of 51+/-4 kJ/mol for the allyl radical, a step-size down for collisional deactivation in argon of 500 cm-1, and lead to the high-pressure rate expression k(allyl-->allene+H)=1.5x10(11)T0.84 exp(-30053/T) s-1 and k(H+allene)-->allyl)=1.2x10(8)T0.69 exp(-1513/T) L mol-1 s-1 over the temperature range 350-1200 K. The uncertainty for the decomposition reaction is estimated to be a factor of 1.3 at 1100 K, but may increase to 1 order of magnitude at the lower temperatures. For the addition reaction, the estimated uncertainties are a factor of 1.5 at 350 K increasing to a factor of 2.5 at 1100 K. The disproportionation to combination ratio for allyl radical under high-temperature conditions is considerably less than 0.005.