We have computed barrier heights of 71.8 ± 2.0 and 216.4 ± 2.0 kJ mol−1 for the reactions CH4 + CH3• → CH3• + CH4 and CH4 + CH3• → H• + C2H6, respectively, using explicitly correlated coupled cluster theory with singles and doubles combined with standard coupled cluster theory with up to connected quadruple excitations. Transition-state theory has been used to compute the respective reaction rate constants in the temperature interval of 250−1500 K. The computed rates for the reaction to ethane are orders of magnitude slower than those used in the mechanism of Norinaga and Deutschmann ( Ind. Eng. Chem. Res. 2007, 46, 3547.) for the modeling of the chemical vapor deposition of pyrolytic carbon.