Abstract: A gaseous-fuelled internal combustion engine and a method of engine operation improve combustion stability and reducing emissions of NOx, PM, and unburned hydrocarbons. The method comprises fuelling an internal combustion engine with hydrogen and natural gas, which can be directly injected into the combustion chamber together or introduced separately. Of the total gaseous fuel delivered to the engine, at least 5% by volume at standard temperature and pressure is hydrogen. For at least one engine operating condition, the ratio of fuel rail pressure to peak in-cylinder pressure is at least 1.5:1. A fuel injection valve introduces the gaseous fuel mixture directly into the combustion chamber. Two separate fuel injection valves could also introduce the methane and hydrogen separately. An electronic controller controls timing for operating the fuel injection valve(s). The engine has a preferred compression ratio of at least 14:1.