酸性气体（英语：Acid gas），是天然气或任何其他气体的混合物，其中含有大量的硫化氢（H₂S）、二氧化碳（CO₂），或类似的污染物。

在炼油厂或天然气处理厂，去除硫醇和/或硫化氢的过程通常被称为脱臭过程，因为他们在产品中不再有酸，而硫醇和硫化氢本身有恶臭的缘故。硫化氢是一种有毒的气体。

Sour gas is natural gas or any other gas containing significant amounts of hydrogen sulfide (H₂S). Natural gas is usually considered sour if there are more than 5.7 milligrams of H₂S per cubic meter of natural gas, which is equivalent to approximately 4 ppm by volume under standard temperature and pressure. However, this threshold varies by country, state, or even agency or application. For instance, the Texas Railroad Commission considers a sour gas pipeline one that carries gas over 100 ppm by volume of H₂S. However, the Texas Commission on Environmental Quality has historically defined sour gas for upstream operations – which requires permitting, reporting, and possibly additional emission controls – as gas that contains more than 24 ppm by volume. Natural gas that does not contain significant amounts of hydrogen sulfide is called "sweet gas."