Optimization of fuel-air mixture strength and distribution is necessary to obtain wider operating range of natural-gas-fueled PCCI engines. From this point of view, three methods of fuel-air mixture preparation: premixed charging, direct injection and intake port injection, were compared in terms of performance, emissions and available load range. Intake port injection with variable timing offers higher engine output than premixed charging at a fixed intake charge temperature. However, the available range of fuelling rate is limited when high EGR rates or high swirl ratios are employed. Cooling effect of injected fuel should be controlled for stabilizing combustion at lean conditions.