The O(D-1) + CH4 reaction has been investigated using a new universal crossed molecular beam apparatus. Hydrogen atom elimination channel has been experimentally observed in this reaction. The pattern of dissociative ionization of the reaction products (from hydrogen loss channel) was compared with that of the methoxy (CH3O) radical produced from the photodissociation of CH3OH at 193 nm which has almost the same total energy deposition as the bimolecular reaction O(D-1) + CH4. The experimental results suggest that the main hydrogen loss channel in the O(D-1) + CH4 reaction should be CH2OH (hydroxymethyl) + H, while the CH3O (methoxy) + H channel is at most a minor reaction channel. This study provides an excellent experimental example of different dynamical behaviors exhibited in the unimolecular and bimolecular reactions of an essentially same chemical system (excited CH3OH) since the O(D-1) + CH4 reaction likely occurs through the insertion mechanism.