Conventional natural gas is not a biofuel. It is a fossil fuel formed over millions of years from ancient organic material buried deep underground. However, there is a renewable version of natural gas, called renewable natural gas (RNG) or biomethane, that is produced from modern organic waste and does qualify as a biofuel. The two are chemically identical, both primarily methane, but their origins and climate impacts are very different.
Why Conventional Natural Gas Is a Fossil Fuel
The natural gas that heats most homes and powers most gas stoves formed from the remains of plants and animals that decomposed millions of years ago. Heat and pressure deep within the Earth slowly converted that organic material into methane trapped in underground rock formations. Extracting and burning it releases carbon that has been locked away for geological timescales, adding new greenhouse gases to the atmosphere. This is the defining characteristic of a fossil fuel, and the vast majority of natural gas consumed in the United States falls into this category.
What Renewable Natural Gas Is
Renewable natural gas is methane captured from organic waste that is decomposing right now, not millions of years ago. When food scraps, animal manure, sewage, or other biological material breaks down without oxygen (a process called anaerobic digestion), it produces a raw gas called biogas. That biogas is roughly 50 to 65 percent methane, mixed with carbon dioxide, hydrogen sulfide, water vapor, and trace contaminants.
To turn biogas into something usable as a direct replacement for fossil natural gas, producers clean and upgrade it by stripping out everything that isn’t methane. The result is pipeline-quality biomethane that can flow through the same pipes, power the same appliances, and fuel the same vehicles as conventional natural gas. No equipment changes are needed on the consumer end.
Where Renewable Natural Gas Comes From
Four main sources supply nearly all the RNG produced in the United States today:
- Landfills. As food waste, paper, wood, and other organic materials decompose in municipal landfills, they generate landfill gas. This is currently the largest source of biogas in the country.
- Livestock farms. Dairy, beef, swine, and poultry manure can be fed into digesters that capture methane instead of letting it escape into the atmosphere. Some farms co-digest other waste streams like fats, oils, greases, and food processing byproducts.
- Wastewater treatment plants. Facilities that treat sewage use anaerobic digestion to break down sewage sludge. Many also co-digest source-separated food waste to boost gas output.
- Stand-alone food waste digesters. These newer facilities accept food scraps and yard waste diverted from landfills, digest them anaerobically, and produce biogas along with a nutrient-rich solid that can be used as fertilizer.
In every case, the feedstock is recent biological material: plants, animals, or products made from them. That is what makes RNG a biofuel rather than a fossil fuel. The carbon in the methane was absorbed from the atmosphere by living organisms in recent years or decades, not millions of years ago.
How the Climate Impact Compares
Because RNG is made from waste that would otherwise decompose and release methane on its own (in a landfill, manure lagoon, or wastewater pond), capturing that methane and burning it for energy can dramatically cut net greenhouse gas emissions. In some cases, particularly with livestock manure, the process prevents methane from escaping uncontrolled into the atmosphere, which can make the fuel’s lifecycle emissions extremely low or even negative on paper.
A large-scale comparative study published in the journal Energy & Environmental Science found that biomethane supply chains achieve 51 to 70 percent lower greenhouse gas emissions than conventional natural gas on average. When produced through anaerobic digestion specifically, the savings range from about 51 to 61 percent compared to fossil gas, depending on the feedstock and how tightly methane leaks are controlled during production. Even in worst-case scenarios with the highest methane leakage rates, biomethane from anaerobic digestion still provided a small emissions reduction of 3 to 13 percent over fossil natural gas.
The wide range matters. A well-managed dairy manure digester with minimal leaks delivers far greater climate benefits than a poorly sealed landfill gas capture system. The climate case for RNG depends heavily on how carefully the production facility is built and maintained.
How RNG Is Used as a Vehicle Fuel
Once upgraded to pipeline quality, RNG can be compressed (CNG) or liquefied (LNG) for use in vehicles, just like fossil natural gas. Compressed RNG is common in transit buses, refuse trucks, and delivery fleets. Liquefied RNG serves long-haul trucking, where energy density matters more. The fueling infrastructure and vehicle engines are identical to those used for fossil CNG and LNG. The only difference is the source of the methane molecule.
This compatibility is one of RNG’s main selling points. Unlike ethanol or biodiesel, which sometimes require engine modifications or blending limits, biomethane slots directly into existing natural gas infrastructure without any adaptation.
The Bottom Line on Classification
If you are asking whether the natural gas piped into your home or used at a gas-fired power plant is a biofuel, the answer is almost certainly no. That gas is fossil-derived. But renewable natural gas, produced from landfill waste, manure, sewage, or food scraps, is a legitimate biofuel. It is chemically the same molecule, methane, but its origin in recently living organic material rather than ancient geological deposits puts it in a fundamentally different environmental category. RNG remains a small fraction of total natural gas supply, so the default assumption for any unlabeled “natural gas” is that it is fossil fuel.