An experimental study is conducted to evaluate the effectiveness of sodium bicarbonate (NaHCO3) powder in extinguishing flames burning hydrocarbon fuels. Experiments are performed formed on flames stabilized in a counterflow burner. Powders with various particle sizes are used. The minimum amount of NaHCO3 powder required to extinguish these flames is measured and compared with previous measurements using CF3Br and N-2. The results show NaHCO3 to be much more effective than CF3Br and N-2 in extinguishing the flames. The calculated equilibrium temperatures of NaHCO3 inhibited flames close to extinction show that NaHCO3 inhibits the flame by chemical mechanisms.