FuelTheGuide
Fuel types

CNG: compressed natural gas as a vehicle fuel

Short answer

CNG is compressed natural gas, mostly methane, sold by weight rather than by volume. It powers dedicated, bi-fuel or converted vehicles and is common only in a handful of countries with well-established infrastructure.

Written by [Author name]. Last reviewed [date]. 4 min read.
In this entry
  1. What CNG is
  2. How it's measured
  3. Which vehicles can use it
  4. Is it cheaper to run?
  5. Where it's common
  6. On FuelTheGuide
  7. Questions and answers
  8. Sources

What CNG is

CNG, compressed natural gas, is mostly methane, the same gas piped into many homes for heating and cooking, compressed to around 200 to 250 times normal atmospheric pressure so a useful amount fits in a vehicle's tank.

It is a different fuel family from petrol, diesel and LPG. It's a gas rather than a liquid, it's stored under much higher pressure than LPG, and it needs its own refuelling equipment.

How CNG is measured and sold

Petrol and diesel are sold by the litre or gallon because they're liquids with a fixed volume at normal pressure. CNG is a compressed gas, so it's usually priced by weight instead.

Kilogram (kg)
The most common way CNG is sold, since it's a gas and doesn't have a fixed volume the way liquid fuels do.
Gasoline gallon equivalent (GGE)
Used in the US: the amount of CNG with the same energy content as one US gallon of petrol, roughly 1 GGE per kg with some variation.
Cubic metre (m³)
Used in some markets, referring to the gas at normal pressure before compression, then converted to an energy or weight basis for pricing.
Weight, not volume

Because CNG is priced by weight in most markets, a price shown "per litre" for CNG isn't meaningful on its own. Always check the unit before comparing it with a liquid fuel's price per litre.

Which vehicles can use it

Not every vehicle can use CNG. It needs a pressurised tank and fuel system built or fitted for the purpose.

Dedicated CNG vehicles
Built to run only on CNG, with a tank sized for the fuel's lower energy density and no petrol backup.
Bi-fuel vehicles
Switch between CNG and petrol, giving a longer range if a CNG station isn't nearby.
Converted vehicles
A petrol vehicle fitted with an aftermarket CNG tank and fuel system, common in markets where CNG is well established.

Is it cheaper to run?

CNG is usually cheaper per unit of energy than petrol, partly because in many markets it is taxed more lightly. As with E85, the fair comparison is cost per distance rather than price per unit, since a CNG vehicle's range per tank and per kilogram differs from a petrol vehicle's range per litre.

See E85 for the same cost-per-distance idea

Where CNG is common

CNG use is concentrated in a handful of markets that built out the infrastructure and vehicle fleet over many years, rather than being spread evenly worldwide.

Pakistan and Iran
Among the largest CNG vehicle fleets in the world, built up over decades of policy support.
Italy and a few other European countries
A long-standing CNG retail network, mostly for passenger cars.
Argentina and Brazil
Large CNG fleets, especially among taxis and light commercial vehicles.
Most of the world
Little or no retail CNG for passenger vehicles, though it may still be used for buses or industrial fleets.

How this shows up on FuelTheGuide

We show CNG as its own grade, priced per kilogram where a country publishes it, separate from petrol, diesel and LPG. Most countries have no CNG data at all, and we show that as a dash, never as a zero.

CNG in the fuel picker
CNG priced per kg, where published
Countries with no CNG data shown as a dash — never zero

CNG appears as its own grade, separate from petrol, diesel and LPG, only for the countries that publish it.

Open the price explorer

Questions and answers

Is CNG the same as LPG?

No. CNG is mostly methane, kept as a gas under high pressure, while LPG is propane and butane, kept as a liquid under much lower pressure. They use different tanks and different refuelling equipment. The US Department of Energy's Alternative Fuels Data Center explains the differences in detail.

Why is CNG usually cheaper than petrol?

Because CNG is taxed more lightly than petrol in many markets. The underlying natural gas commodity is often cheaper than crude-derived fuels, and in many countries the excise duty on CNG is lower, sometimes as an incentive to shift towards lower-emission fuels.

Do CNG vehicles have a shorter range than petrol ones?

Usually, yes. CNG tanks hold less energy than a petrol tank of similar size, partly because of the weight and volume needed to store it safely under pressure. Bi-fuel vehicles carry a petrol tank as backup, which extends effective range.

Is CNG safe?

CNG vehicles have a strong safety record. The tanks are built to withstand significant impact without rupture, and because methane is lighter than air it disperses quickly if there is a leak, rather than pooling on the ground like petrol vapour or LPG. The US DOE Alternative Fuels Data Center covers CNG vehicle safety in more detail.

Sources and further reading

Guide · 5 min read

Petrol or diesel: which costs less to run?

Price per litre is only half of it. Fuel use, taxes and distance decide. The same cost-per-distance logic applies to CNG.

Read the guide