CNG stands for compressed natural gas. It is pipeline natural gas, about 90 to 95 percent methane, compressed to 3,000 or 3,600 psi and stored in a high-pressure cylinder on the vehicle. A spark-ignition engine burns it much like gasoline. It is sold by the gasoline gallon equivalent (GGE), it is usually cheaper than gasoline per GGE, it burns cleaner, and it is available at 674 public stations in the United States.
What is actually in the tank
Natural gas from the pipeline is mostly methane (CH4) with small amounts of ethane, propane, nitrogen and carbon dioxide. A CNG station takes that gas, dries it, filters it and runs it through a multi-stage compressor into storage vessels at up to 4,500 psi. When you fill, the dispenser meters gas from storage into your vehicle's cylinder until the cylinder reaches its service pressure, 3,600 psi on anything built in the last twenty years, 3,000 psi on some older vehicles and stations.
Because it is a gas, it takes a lot of space: a 3,600 psi cylinder holds roughly a quarter of the energy of a gasoline tank of the same volume. That is the single biggest engineering trade-off of the fuel and the reason CNG cars carry their tank in the trunk and CNG trucks wear cylinders behind the cab.
Methane has an octane rating around 130, well above premium gasoline, which is why a dedicated natural gas engine can run higher compression and why a bi-fuel engine loses a little power on gas: the engine is tuned for gasoline and cannot take full advantage.
GGE and DGE: how CNG is sold
| GGE (gasoline gallon equivalent) | The amount of CNG with the energy of one gallon of gasoline: 5.66 pounds of natural gas by the federal definition. Light-duty stations price in GGE. |
| DGE (diesel gallon equivalent) | The amount with the energy of one gallon of diesel: 6.38 pounds. Truck stops and heavy-duty stations price in DGE, and truck tank packages are rated in DGE. |
| Converting | 1 DGE is about 1.13 GGE. A price of $2.50 per GGE is about $2.82 per DGE. |
| Federal excise tax | CNG is taxed at 18.3 cents per GGE, the same rate as a gallon of gasoline. LNG is taxed at 24.3 cents per DGE, matching diesel. |
Because the unit is defined by energy, miles per GGE in a CNG vehicle are directly comparable with miles per gallon in a gasoline one, and the price guide compares them that way.
CNG compared with gasoline, diesel, LNG and propane
| CNG | LNG | Propane (autogas) | Gasoline / diesel | |
|---|---|---|---|---|
| State in the tank | Gas at 3,600 psi | Liquid at −260°F, low pressure | Liquid at 100 to 200 psi | Liquid |
| Energy per tank volume | About 25% of gasoline | About 60% of diesel | About 73% of gasoline | 100% |
| Public U.S. stations | 674 | 21 | Around 2,500 (many U-Haul) | Well over 100,000 |
| Typical use | Cars, pickups, refuse, transit, regional trucks | Long-haul trucks | School buses, delivery vans, forklifts | Everything |
| Price basis | Per GGE or DGE | Per DGE | Per gallon | Per gallon |
CNG vs LNG goes deeper on the two natural gas fuels. Propane is a different fuel with its own network and is out of scope for this site.
Where the gas comes from
Almost all of it is domestic U.S. pipeline gas, which is why the price tracks the U.S. natural gas market rather than crude oil. A growing share is renewable natural gas (RNG): methane captured from landfills, dairy manure digesters and wastewater plants, cleaned to pipeline quality and injected into the same pipes. About 69% of public CNG stations report dispensing RNG. The RNG guide explains what that badge does and does not mean.
Safety
- The cylinder. CNG cylinders are built to the NGV2 standard and federal FMVSS 304, drop-tested, fire-tested and shot at during certification. They carry a pressure relief device that vents gas in a fire rather than letting pressure build. Every cylinder has an expiration date (15 to 25 years) and needs a visual inspection every 3 years or 36,000 miles.
- The gas. Methane is lighter than air and disperses upward if it leaks, unlike gasoline vapor or propane, which pool. Its ignition range is narrow (about 5 to 15 percent in air) and its ignition temperature is high.
- The fill. The nozzle locks onto the receptacle and seals before gas flows; nothing is exposed during a fill. The fueling guide walks through it.
- Parking garages. Some older garages posted bans on CNG vehicles. Most U.S. jurisdictions now treat NGVs like any other vehicle, but check local signage in tunnels and underground structures.
Who uses CNG
By fuel volume, fleets: refuse haulers, transit agencies, port drayage, regional tractor fleets, utility and municipal trucks, school buses, taxis and airport shuttles. By vehicle count, a long tail of used Honda Civic GX owners and bi-fuel pickup owners. The vehicles pages cover what has been sold, and the directory shows the network that serves them.
FAQ
What does CNG stand for?
Compressed natural gas. It is pipeline natural gas, mostly methane, compressed to 3,000 or 3,600 psi so a vehicle can store enough of it to be useful.
Is CNG the same as propane?
No. Propane (LPG or autogas) is a different hydrocarbon that stores as a liquid at low pressure. CNG is methane stored as a gas at very high pressure. They use different tanks, different engines and different stations.
What is a GGE?
A gasoline gallon equivalent, the amount of CNG that holds the same energy as one gallon of gasoline, defined federally as 5.66 pounds of natural gas. CNG stations price by the GGE, or by the diesel gallon equivalent (DGE, 6.38 pounds) at truck stops.
Is CNG safe?
CNG cylinders are certified by drop, fire and gunfire tests, carry pressure relief devices, and must be inspected every 3 years. Methane is lighter than air and disperses if it leaks. The safety record of natural gas vehicles is at least as good as gasoline vehicles.
How many CNG stations are there?
The DOE lists about 700 public CNG stations in the United States and roughly as many private fleet-only sites. The current public count is shown on the homepage of this site and refreshed weekly.
Find a station
Every public CNG station, with the badges this guide explains.