The introduction of small quantities of tetrachloromethane (TCM) into the feedstream in the oxidation of ethane with nitrous oxide on 12-molybdophosphoric acid (HPMo) supported on silica increases the conversion but has little effect on the selectivities. in the presence of TCM the primary products appear to be ethylene, acetaldehyde and ethyl chloride. Studies of the effects of loading, time-on-stream, contact time and reaction temperature provide evidence for the importance of a loading corresponding approximately to a monolayer of HPMo, the HPMo anion in the production of acetaldehyde and TCM in both the production of ethyl radicals and the selectivity to acetaldehyde.