Experimental and theoretical data are provided for a set of 11 pericyclic reactions of unsaturated hydrocarbons. Literature experimental data are evaluated and standardized to ΔH^⧧_0K for comparison to theory. Hartree−Fock, MP2, CASSCF, CASPT2, density functional theory (B3LYP, BPW91, MPW1K, and KMLYP functionals), and CBS-QB3 transition-structure geometries, activation enthalpies and entropies, and reaction enthalpies and entropies for these reactions are reported and are compared to experimental results. For activation enthalpies, several density functionals rival CASPT2 and CBS-QB3 for closest agreement with experiment, while CASPT2 and CBS-QB3 provide the most accurate heats of reaction. Transition-structure geometries are reproduced well by all methods with the exception of the Cope rearrangement and cyclopentadiene dimerization transition structures.