Flame propagation velocity is one of the important characteristics in the study of combustion of gaseous hydrocarbons with air. It affects the efficiency and stability of many combustion systems, such as furnaces, combustion engines, and gas turbines. The composition of the fuel, including the number of carbon atoms in the hydrocarbon molecule, has a direct influence on flame behavior and propagation velocity. When moving from short-chain hydrocarbons such as methane (CH_4) to ethane (C_2H_6), propane (C_3H_8), and butane (C_4H_{10}), the physical and chemical properties of the fuel change, as do the reaction mechanisms during combustion. Therefore, the effect of increasing the number of carbon atoms on flame velocity is not linear. The flame velocity of some higher hydrocarbons may be higher than, or close to, that of methane, depending on the fuel-to-air ratio, temperature, and pressure. Experimental measurements show that ethane can have a higher laminar burning velocity than methane under certain conditions, while the flame velocities of propane and butane are relatively close to these values. Some measurements indicate a tendency for flame velocity to decrease when moving toward heavier hydrocarbons. This behavior is related to changes in chemical reaction rates, heat and mass transfer, flame temperature, and the transport properties of the fuel. An increase in the number of carbon atoms also increases the amount of oxygen required for complete combustion per mole of fuel. For example, methane requires two moles of O_2 per mole of fuel, whereas propane requires five moles of O_2. However, the required amount of oxygen alone does not determine flame velocity, since flame propagation is also affected by chemical kinetics and the formation of active radicals such as H, O, and OH. Another important factor is the equivalence ratio. The flame velocity generally reaches its maximum near the stoichiometric mixture and decreases when the mixture becomes excessively lean or rich. Increasing the temperature of the unburned mixture generally increases flame velocity, whereas increasing pressure often decreases the laminar burning velocity. In conclusion, the number of carbon atoms is an important factor affecting flame propagation velocity; however, its effect cannot be considered independently of other operating and chemical factors. Therefore, comparisons of flame velocity among methane, ethane, propane, and butane should be performed under similar conditions of temperature, pressure, and equivalence ratio to obtain accurate and comparable results