The thermochemistry of the reaction of dimethyl sulfoxide with OH, O-2 and O-3 was investigated at a highly correlated ab initio level of theory. For the OH radical, channels that lead to CH3S(O)CH2 + H2O, CH3S(O)OH + CH3 and CH3SO + CH3OH products are spontaneous. All possibilities studied for the reaction with O-2 are non-spontaneous. The reaction channels with O-3 producing CH3SO + CH3OOO and CH3S(O)(2)CH3 + O-2 are thermodynamically favorable. The performance of the IB method for reaction energies containing sulfur compounds was investigated, and the results show that this extrapolation is not as efficient as expected, producing results of accuracy intermediate between cc-pVTZ and cc-pVQZ levels. (C) 2004 Elsevier B.V. All rights reserved.