Cyclic and aromatic hydrocarbons are important components of usual commercial fuels, with C6-rings being among the most abundant cyclic structures. The combustion chemistry of C6-rings involves different levels of unsaturation, either as initial fuels (aromatics, naphtenes) as intermediates formed during their combustion. The ignition delays of cyclohexane, cyclohexene, 1,3-cyclohexadiene (13-CHD) and 1,4-cyclohexadiene (14-CHD) were systematically evaluated using experiments and kinetic modeling. Shock tube experiments were performed at high-temperature (above 1200 K) and for mean pressures of 6 atm. A detailed chemical kinetic model was developed that includes the combustion chemistry of the four cyclo-C 6 fuels. Electronic structure calculations were performed at the CCSD(T)/CBS//B2PLYP-D3 level of theory on the pericyclic reactions of the unsaturated fuels. Pressure-dependent rate coefficients were computed by solving the master equation, and included in the mechanism. Results revealed the experimental ranking of reactivity: cyclohexene > 14-CHD > cyclohexane > benzene ≈13-CHD. Kinetic analyses of the difference of reactivity revealed that pericyclic reactions play a major role in the initial decomposition of the unsaturated fuels.