[en] The abundances of simple oxygen-bearing interstellar molecules in warm (Tapproximately-greater-than40 K), diffuse, and moderately thick clouds are calculated on the basis of binary gas phase reactions. The most important reactions are ion-molecule, charge exchange, and dissociative recombination reactions, as suggested mainly by earlier workers. The progenitor of these molecules in diffuse clouds is the cosmic ray produced H⁺ ion, working through the charge exchange reaction with O. The ionization of H⁺ and He⁺ are also discussed. Dissociative charge exchange of He⁺ with H₂ is an important source of H⁺ in regions of large fractional abundance of H₂, as well as an important destruction mechanism for He⁺ even for small f (approximately-greater-than0.1). The calculated molecular abundances are consistent with some of the available observational information