From 910 to 1089°K, at pressures of 20 to 36 mm, the pyrolysis of ethylbenzene in a toluene carrier flow system occurs primarily by three reactionsThe Arrhenius equation for the reaction [1], logk1(s−1) = 14.7 − (70 100/2.3RT), is in agreement with a previous aniline carrier study and with thermochemical calculations. Reaction [11] is surface dependent and yields widely scattered results. For experiments in a conditioned quartz vessel, logk11(s−1) = 9.06 − (51 700/2.3RT). Values ofk1andk12are unaffected by the nature of the surface and by changes in the surface-to-volume ratio. The rate constants for reaction [12] are somewhat scattered, but yield the approximate equation logk12(s−1) = 12.7 − (64 000/2.3RT).E1should possibly be increased by about 1 kcal to allow for the effect of reaction [−1], the recombination of methyl and benzyl species.