Studies of unimolecular dissociation (MIKES) of ions formed in a chemical ionization ion source show that under CI conditions, the reaction of CH3+ with CH3OH or CH3OCH3 leads to the covalent structures (CH3)(2)-OH+ or(CH3O+. In contrast a FT-ICR study indicates that these reactions lead either to covalent structures by C-O bond formation and to [CH3+/CH3OH] or [CH3+/CH3OCH3] ion-neutral complexes. Ab initio calculations confirm that such complexes correspond to minima on the potential energy surface. Their geometries correspond to a species in which a hydrogen of the CH3+ cation is weakly bonded to the oxygen of the neutral. The interaction energies are similar to 20 kcal/mol.