Fuel gas is any gaseous substance burned to produce heat or energy. The most common example is natural gas, which heats roughly half of American homes, but the category also includes propane, butane, hydrogen, biogas, and several industrial byproduct gases. What unites them is simple: they combust when mixed with air, releasing energy you can use for cooking, heating, manufacturing, or generating electricity.
What Fuel Gas Is Made Of
Most fuel gases are hydrocarbons, meaning they’re built from hydrogen and carbon atoms. Natural gas is mostly methane (CH₄), the simplest hydrocarbon: one carbon atom bonded to four hydrogen atoms. Raw natural gas pulled from a well also contains ethane, propane, butanes, pentanes, water vapor, and impurities like hydrogen sulfide, nitrogen, and carbon dioxide. Processing strips out those impurities before the gas reaches your home.
Propane and butane, sold as liquefied petroleum gas (LPG), are heavier hydrocarbons that can be compressed into liquid form for storage in portable tanks. Hydrogen is the outlier: no carbon at all, just H₂, which means it produces only water when it burns. Biogas, produced from decomposing organic waste, is a renewable mixture of methane and carbon dioxide. And synthesis gas (syngas), made by heating biomass or coal in a low-oxygen environment, contains carbon monoxide, hydrogen, and methane.
Energy Content Varies Widely
Not all fuel gases pack the same punch. Energy content is typically measured in BTUs (British thermal units) per cubic foot, and the differences are significant:
- Methane (natural gas): about 1,000–1,030 BTU per cubic foot
- Propane: about 2,500 BTU per cubic foot
- Butane: about 3,200 BTU per cubic foot
This is why a propane grill heats up faster than a natural gas one using the same volume of fuel. Butane is even more energy-dense, which makes it useful in portable applications like camping stoves and lighters. On the other end of the spectrum, industrial byproduct gases like blast furnace gas contain far less energy, sometimes as little as 3.5 MJ per cubic meter, because they’re diluted with large amounts of nitrogen and carbon dioxide.
Industrial Byproduct Gases
Steel mills and coke plants generate enormous volumes of combustible gas as a side effect of their core processes. These byproduct gases are too valuable to waste, so they’re captured and burned on-site or sold.
Blast furnace gas (BFG) is produced during iron smelting. It contains 18–38% carbon monoxide, 48–61% nitrogen, and smaller amounts of hydrogen and carbon dioxide. All that nitrogen makes it a low-energy fuel, with a heating value of roughly 3.5–5.0 MJ per cubic meter. Steelmakers use it in reheating furnaces and power generation, often blending it with richer gases to boost its energy content.
Coke oven gas (COG) is a different story. Produced when coal is baked into coke, it’s surprisingly rich: 53–60% hydrogen and 23–28% methane. After purification to remove tar, ammonia, and hydrogen sulfide, coke oven gas delivers 16–20 MJ per cubic meter, making it a medium-energy fuel useful throughout the steel production chain. One tonne of coking coal yields roughly 310–360 cubic meters of purified gas.
Why You Can Smell a Gas Leak
Natural gas and propane are both naturally odorless and colorless, which would make leaks impossible to detect without instruments. To solve this, gas utilities add chemical odorants before the gas enters the distribution system. The most common is methyl mercaptan, a compound with a strong rotten-cabbage smell that humans can detect at concentrations as low as 0.002 parts per million. That extreme sensitivity is the whole point: you’ll notice a leak long before the gas concentration becomes dangerous.
One limitation worth knowing: prolonged exposure can cause olfactory fatigue, meaning your nose stops registering the smell over time. This is why gas detectors are recommended in addition to relying on your sense of smell, particularly in enclosed or industrial spaces.
Carbon Emissions by Fuel Type
Fuel gas generally burns cleaner than coal or oil, but “cleaner” is relative. Natural gas produces about 53 kilograms of CO₂ per million BTU of energy. Propane is slightly higher at roughly 63 kilograms per million BTU. Both are substantially lower than coal, which emits around 95 kilograms per million BTU, and lower than most liquid petroleum fuels as well.
Hydrogen stands apart because burning it produces zero carbon dioxide at the point of use. The carbon question for hydrogen depends entirely on how it’s produced: if made using renewable electricity to split water, the full lifecycle emissions are near zero. If made from natural gas (which is how most hydrogen is currently produced), the upstream emissions can be significant.
How Fuel Gas Reaches You
Residential natural gas arrives through a network of underground pipelines at low pressure, typically 1–3 kilopascals. That’s a gentle flow, just enough to feed your furnace, stove, and water heater through small-diameter pipes. Industrial customers receive gas at much higher pressures to meet the enormous volumes required for manufacturing, power generation, and chemical processing.
Propane and butane take a different path. Because they liquefy under moderate pressure, they’re stored in tanks and cylinders rather than piped continuously. This makes LPG practical for rural homes that aren’t connected to a natural gas grid, as well as for portable applications.
Renewable Fuel Gas Is Growing Fast
Biogas and biomethane (also called renewable natural gas, or RNG) are emerging as lower-carbon alternatives. Biogas is produced when microorganisms break down organic material like food waste, manure, or sewage in the absence of oxygen. When that raw biogas is purified to remove CO₂ and contaminants, the resulting biomethane is chemically identical to fossil natural gas and can flow through existing pipelines without any infrastructure changes.
The United States is the world’s largest producer of biomethane, with output growing 2.2 times since 2020. Transportation has been the primary driver: RNG use in vehicles has increased an average of 28% year over year over the past five years. In Europe, EU biomethane production rose 14% in 2024, with Germany, France, Italy, Denmark, and the Netherlands accounting for 93% of output. France is introducing a blending mandate for biomethane grid injection in 2026, and India has launched a compressed biogas blending mandate for transport and domestic piped gas.
Globally, combined biogas and biomethane production is expected to grow 22% from 2025 to 2030, according to the International Energy Agency. While biogas accounted for about half of output in 2023, 95% of new plants coming online are producing biomethane instead, reflecting a clear shift toward pipeline-ready renewable gas.
Hydrogen Blending Into Gas Networks
One of the more active areas of development is blending hydrogen into existing natural gas pipelines. The U.S. Department of Energy has found that blends of up to about 15% hydrogen require only modest pipeline modifications. This approach lets utilities reduce the carbon intensity of their gas supply without replacing infrastructure or requiring customers to change their equipment. Several pilot projects around the world are testing various blend ratios to determine the practical limits for appliances, meters, and pipeline materials.
Beyond blending, some regions are exploring dedicated hydrogen pipelines for industrial users who need pure hydrogen for processes like refining or ammonia production. Currently about 1,600 miles of hydrogen pipeline exist in the United States, concentrated near petrochemical facilities along the Gulf Coast.