Transition structures for CH 4 + OH --→ CH 3 + H 2 O and CD 4 + OH --→ CD 3 + HDO can have two possible conformers, namely eclipsed and staggered, which are linked by the methyl torsion. Past studies using Hartree-Fock, MP-SAC2, and CCSD(T)-F12a identified the staggered conformer as the sole transition structure conformer with one imaginary frequency, whereas MP2 calculations indicated the eclipsed conformer as the only transition structure conformer. However, in contrast to both of the above scenarios, M08-HX and CNEO-M08-HX predict that both the eclipsed and the staggered conformers are transi-tion structures, each with only one imaginary frequency, and that the eclipsed conformer is slightly lower in energy. To account for the multistructural torsional anharmonicity, we used the multistructural method based on a coupled torsional potential (MS-T(C)) with a total of six of minima for the methyl torsion, including two distinguishable minima. Therefore, technically speaking, the calculations for these reactions are by multistructural CVT/SCT (MS-CVT/SCT) 153 and multistructural CNEO-TST (MS-CNEO-TST).