There are two initiation steps involved in the combustion of dimethyl ether (DME), one involving C-O bond fission and the other involving hydrogen abstraction by molecular oxygen. The kinetics and thermodynamics of C-O bond fission were explored computationally in a previous paper. The present paper addresses the competing process-hydrogen abstraction by molecular oxygen. db initio molecular orbital calculations are used to study the structures and energetics of the reactants, products, and the transition state for the CH3OCH3 + O-2 reaction. The calculations predict a barrier for hydrogen abstraction from CH3OCH3 by O-2 of 47.4 kcal mol(-1). This is lower than the barrier height for C-O bond fission previously calculated to be 81.1 kcal mol(-1). The results support values used in current models for the combustion of DME. Moreover, an examination of rates for C-O bond fission versus hydrogen abstraction by O-2 suggests that the bimolecular process is the dominant pathway.