The use of decomposed methanol,i.e., hydrogen and carbon monoxide, in spark-ignition engines is reviewed. The emphasis is on onboard decomposition and the paper docs not deal with engines fueled by stored hydrogen. The paper concentrates mostly on the experimental work performed using catalytically decomposed methanol, where the methanol is used as a hydrogen carrier. The greatest potential for this type of engine, besides the low energy consumption, lies in the low emissions of nitrogen oxides when running at lean air/fuel ratios.