The global potential energy surfaces of the (CH3O2)(2) system have been calculated at the B3LYP/6-311G(d,p) level of theory. The results show that the most stable intermediate out of the nine possible open chain and cyclic dimers of CH3O2 is the singlet (CH3O2)(2) chain-structure with C1 symmetry, which lies 5.36 kcal/mol below the reactants. The transition states for the production of CH3O + CH3O + O-2 and CH3OOCH3 + O-2 have been calculated at the same level of theory in order to fully explore the potential energy surface for this reaction. (c) 2005 Published by Elsevier B.V.