Yes, natural gas is a fossil fuel. It forms from the buried remains of ancient plants and animals over millions of years, placing it in the same category as coal and petroleum. What sets it apart from other fossil fuels is its chemical makeup and how it burns, which gives it a different (though still significant) climate footprint.
Why Natural Gas Qualifies as a Fossil Fuel
A fossil fuel is any energy source formed from decomposed organic matter trapped underground for millions of years. Natural gas checks every box. Millions to hundreds of millions of years ago, the remains of plants and tiny marine organisms like diatoms accumulated in thick layers on the earth’s surface and ocean floors, mixed with sand, silt, and calcium carbonate. Over time, additional sediment buried those layers deeper and deeper.
As burial continued, rising temperatures transformed the organic material. When temperatures in the rock exceeded about 120°C (250°F), the organic remains began to “cook,” producing both oil and natural gas. This process takes millions of years just to reach those temperatures, then millions more to generate enough gas to fill underground reservoirs. At even higher temperatures, above roughly 150°C (300°F), the process shifts almost entirely toward gas production rather than oil. Some natural gas also forms at shallower depths, less than about 2,000 feet, through bacterial breakdown of organic matter rather than heat.
What Natural Gas Is Made Of
Natural gas is 70 to 90 percent methane, with smaller amounts of ethane (up to 14 percent in some deposits), propane (up to 5 percent), and trace heavier hydrocarbons like butane and pentane. Raw natural gas straight from the ground also contains impurities: nitrogen, carbon dioxide, hydrogen sulfide, water vapor, and even small amounts of helium and argon. These get stripped out during processing before the gas reaches your stove or furnace.
How It Gets Out of the Ground
Conventional natural gas sits in distinct underground reservoirs, relatively easy to tap with a standard well. Unconventional natural gas, particularly shale gas and tight gas, is spread throughout wide rock formations and doesn’t flow freely. Extracting it requires hydraulic fracturing, commonly called fracking. In this process, a high-pressure mixture of water and sand is pumped underground to crack open the rock. When the pressure is released, some fluid flows back to the surface, but the sand stays behind to prop the fractures open and let gas escape.
The growth of fracking over the past two decades has dramatically expanded natural gas production, especially in the United States, turning previously inaccessible formations into major gas sources.
How Its Emissions Compare to Coal and Oil
Burning natural gas produces about 117 pounds of CO2 per million BTU of energy. That’s roughly 45 percent less than coal, which emits about 212 pounds per million BTU, and about 25 percent less than gasoline at 156 pounds per million BTU. This lower carbon intensity is the main reason natural gas is sometimes called a “bridge fuel” between coal and renewables.
But CO2 from combustion isn’t the full picture. Methane itself is a powerful greenhouse gas. The latest IPCC assessment rates fossil methane at 29.8 times more potent than CO2 over a 100-year period. Leaks during drilling, processing, and pipeline transport release unburned methane directly into the atmosphere, which narrows the climate advantage over coal. How much it narrows depends on leak rates, which vary widely by region and operator.
How It Differs from Renewable Gas
There is a non-fossil version of methane. Renewable natural gas, also called biomethane, comes from the decomposition of organic waste: landfills, animal manure, wastewater, and food scraps. Chemically, it’s the same molecule. The difference is timing. Fossil natural gas releases carbon that’s been locked underground for millions of years, adding new CO2 to the atmosphere. Biomethane recycles carbon that was already in the atmosphere recently, making its net contribution to warming much smaller.
Studies comparing the full life cycle of biomethane to fossil natural gas find greenhouse gas savings of roughly 42 to 65 percent. That’s a meaningful reduction, though biomethane isn’t the lowest-emission energy option available and currently represents a tiny fraction of total gas supply.
The “Natural” in the Name
The word “natural” can be misleading. It distinguishes the gas from manufactured gas (which was historically produced from coal) rather than making any claim about environmental friendliness. Some climate scientists and advocates have pushed to call it simply “methane” or “fossil gas” to make its climate impact clearer. Regardless of the label, natural gas is a hydrocarbon fuel formed from ancient biological material underground. By every geological and chemical definition, it is a fossil fuel.