Fuel gas is any one of a number of fuels that under ordinary conditions are gaseous. Most fuel gases are composed of hydrocarbons (such as methane or propane), hydrogen, carbon monoxide, or mixtures thereof. Such gases are sources of energy that can be readily transmitted and distributed through pipes.

Fuel gas is contrasted with liquid fuels and from solid fuels, although some fuel gases are liquefied for storage or transport (for example, autogas). While their gaseous nature has advantages, avoiding the difficulty of transporting solid fuel and the dangers of spillage inherent in liquid fuels, it also has limitation. It is possible for a fuel gas to be undetected and cause a gas explosion. For this reason, odorizers are added to most fuel gases. The most common type of fuel gas in current use is natural gas.