Engine-out and post-catalyst emissions of ammonia, hydrocarbons, nitric oxide, carbon monoxide, and nitrous oxide are measured for an ammonia and gasoline dual fueled spark ignition engine. An ordinary three-way catalytic converter can be used to clean up these emissions. The clean-up region occurs between stoichiometric and 0.2% rich. Ordinary exhaust gas oxygen sensors are usable with ammonia and gasoline in much the same way as they are with gasoline alone.