Abstract The decomposition of ortho-benzyne radicals (o-C6H4), generated from the dissociation of a new precursor, fluorobenzene (C6H5F), has been investigated in a diaphragmless shock tube in a combined laser schlieren densitometry, LS, (P2=30±2, 59±3, 121±5Torr, 2050<T2<2980)/time-of-flight mass spectrometry, TOF-MS (P5=1150±200Torr, 2300<T5<2800K) study. The LS density gradient profiles were simulated, and excellent agreement was found between simulations and experimental profiles. Rate coefficients for C6H5F→o-C6H4+HF, o-C6H4→C4H2+C2H2, and o-C6H4→C6H3+H were obtained. Good agreement with Xu et al. [Proc. Combust. Inst., 31(2007) 231-239] with respect to the o-benzyne dissociation branching ratio was found. However a strong pressure dependence was also observed in o-benzyne dissociation which was not seen by Xu et al. For o-C6H4→C4H2+C2H2: k2a,120Torr=(1.2±0.4)×1063T−14.27 exp(−52,710/T) k2a,60Torr=(1.4±0.5)×1060T−13.595 exp(−50,538/T), k2a,30Torr=(4.0±1.3)×1057T−13.015 exp(−48,628/T) s−1. The inclusion of high temperature o-benzyne abstraction reactions is necessary to simulate the reacting system, and we report estimates of the rate of o-C6H4+C6H5F.