The elementary reaction paths of CH₃S + O₂ abstraction and association reaction systems are calculated using a wide range of computation chemistry theory levels including B3LYP with 6-311++G(d,p), 6-311++G(2d,p), 6-311++G(3df,2p), and 6-311++G(3df,3pd) basis sets. Sulfur is in a lower row of the periodic table than carbon and oxygen, so other density function and ab initio calculations are studied to try and determine an accurate potential curve and a density functional method for use on larger sulfur molecules. These include: CCSD(T)/6-311G(d,p)//MP2/6-31G(d,p), QCISD/6-31G(d), B3P86/6-311G(2d,2p)//B3P86/6-31G(d), B3PW91/6-311++g(3df,2p), G2, G3, G3MP2, G3B3, G3MP2B3, and CBS-QB3. The enthalpies of formations of reactants, four intermediates and five product sets are also determined and where possible compared with literature values using results from total energies at CBS-QB3 level with isodesmic work reactions. Contributions to the entropy and the heat capacity from translation, vibration, and external rotations are calculated using the rigid-rotor-harmonic-oscillator approximation based on the B3LYP/6-311++G(d,p) structures. Hindered internal rotational contributions to entropies and heat capacities are calculated by summation over the energy levels found using the internal rotor potential from B3LYP/6-31G(d,p) calculation level. Rate constants for the chemical activation and dissociation reactions are estimated as a function of temperature and pressure using quantum RRK analysis for k(E) and master equation for pressure fall-off.