The balanced chemical equation for the complete combustion of propane ($\text{C}_3\text{H}_8$) is: $\text{C}_3\text{H}_8(g) + 5\text{O}_2(g) \rightarrow 3\text{CO}_2(g) + 4\text{H}_2\text{O}(l)$ According to Gay Lussac's law of gaseous volumes, gases combine or are produced in a chemical reaction in a simple ratio by volume, provided all gases are at the same temperature and pressure . From the stoichiometry of the balanced equation, $1 \text{ volume}$ of propane gas requires $5 \text{ volumes}$ of oxygen gas for complete combustion. Therefore, $1 \text{ L}$ of propane gas will require $5 \times 1 \text{ L} = 5 \text{ L}$ of oxygen gas.