The kinetics and thermochemistry of the pent-1-en-3-yl radical reaction with molecular oxygen (CHCHCHCHCH + O) has been studied by both experimental and computational methods. The bimolecular rate coefficient of the reaction was measured as a function of temperature (198-370 K) and pressure (0.2-4.5 Torr) using laser photolysis-photoionization mass-spectrometry. Quantum chemical calculations were used to explore the potential energy surface of the reaction, after which Rice-Ramsperger-Kassel-Marcus theory/master equation simulations were performed to investigate the reaction. The experimental data were used to adjust key parameters, such as well depths, in the master equation model within methodological uncertainties. The master equation simulations suggest that the formation rates of the two potential RO adducts are equal and that the reaction to QOOH is slower than for saturated hydrocarbons. The initial addition reaction, CHCHCHCHCH + O, is found to be barrierless when accounting for multireference effects. This is in agreement with the current experimental data, as well as with past experimental data for the allyl + O reaction. Finally, we conducted numerical simulations of the pent-1-en-3-yl + O reaction system and observed significant amounts of penta-1,3-diene being formed under engine-relevant conditions.