Com. gas oil was modified by addn. of a Fe catalyst consisting of a Fe soap and Fe(OH)(3) (0.01% by mass) and tested for CO, CO2 and hydrocarbon emissions during combustion in a self-ignition engine (10-30 kW). Addn. of the catalyst resulted in a significant redn. of CO and hydrocarbon contents in the of-gases (at engine load 20-30 kW) and a decrease in the oil consumption.