The input data for the OH + CH3SH reaction, with 18 degrees of freedom, 35 electrons and the presence of two reactive paths, requires a very high computational cost, where the quality of the electronic structure calculations, strongly dependent on the correlation method and basis set, will determine the accuracy of the new PES. By using ab initio calculations of quality coupled-cluster with single, double, and triple (perturbative) excitations with basis sets of triple-zeta quality, CCSD(T)/cc-pVTZ, which represents a standard in this type of reactive process, all stationary points for the R1 and R2 paths were located and characterized (by using the corresponding vibrational frequencies). In addition to the reactants, products, saddle points and intermediate complexes, 90 points describing each minimum energy path were also calculated. In this case, due to the existence of two channels, the high computational cost and the very flat entrance channel for both paths, a lower level was used, second order Møller-Plesset perturbation theory, MP2, with the 6-31G(d,p) basis set. Finally, in order to improve the energetic description, the explicitly correlated method with a larger basis set, CCSD(T)-F12/aug-cc-pVTZ was used based on the previous optimized geometries. These high level electronic structure calculations were performed using the Gaussian 16 and Molpro codes.