A study of the oxidation of ethylbenzene has been performed in a jet-stirred reactor (JSR) at quasi-atmospheric pressure (800 Torr), at temperatures ranging 750–1100 K, at a mean residence time of 2 s and at three equivalence ratios ϕ (0.25, 1, and 2). Reactants and 25 reaction products were analyzed online by gas chromatography after sampling in the outlet gas. A new mechanism for the oxidation of ethylbenzene was proposed whose predictions were in satisfactory agreement with the measured species profiles obtained in JSR and with flow reactor data from the literature. A flow rate analysis has been performed at 900 K showing the important role of the combinations with HO2 radicals of resonance stabilized radicals obtained from ethylbenzene by H-atom abstractions. Other important reactions of ethylbenzene are the ipso-additions of H- and O-atoms and of methyl radicals to the aromatic ring.