A study was conducted to understand the effects of dilution and co-flow on the sooting characteristics of hydrocarbon fuels. Measurements of the critical mass flow rate of a fuel at the threshold of smoking and the mass flow rate of the dilution gas (nitrogen) required to suppress smoking at several fuel flow rates were obtained. At the same time, the radiation emission and flame heights were also measured. Also recorded was the axial radiation profile at the critical fuel mass flow rate. Three fuels of differing sooting propensities were used: ethylene (C2H4), propylene (C3H6), and propane (C3H8). A 3.2 mm ID burner was employed. The results showed that propylene had the highest critical fuel flow rate and the highest nitrogen dilution required to suppress smoking, followed by ethylene and propane. Besides, propylene produced the highest flame radiation, followed by ethylene and propane. The variation of nitrogen flow rate required for smoke suppression with fuel flow rate exhibited a skewed bell shape for all fuels. The co-flow had no significant effect on flame soot liberation characteristics.