CNG is Compressed Natural Gas, which is mainly methane compressed at a pressure of 200 to 248 bars. LPG is Liquefied Petroleum Gas, a mixture of propane and butane liquefied at 15 °C and a pressure of 1.7 - 7.5 bar. Some variants of LPG are primarily propane so LPG is often colloquially called propane. CNG is cheaper and cleaner, but LPG has a higher calorific value. Distribution is easier for natural gas over long distances via pipelines.

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Constituents Methane Propane and Butane
Source Obtained from natural gas-and-condensate wells, oil wells, coal bed methane wells. Automatically generated from gas fields when natural gas is extracted from the reservoir. By-product of cracking process during crude-oil refining.
Uses Substitute for gasoline in automobiles. Heating and cooking in homes, refrigeration, industrial, agricultural, catering and automobile fuel.
Environmental effects Releases lesser greenhouse gas. Releases CO2 which is a greenhouse gas but is cleaner when compared to gasoline.
Properties It is lighter than air and hence disperses quickly in the event of spillage. Highly inflammable. It is heavier than air and on leakage will settle to ground and accumulate in low lying areas.
Safety Easily disperses, hence risk of ignition is minimized. Since it is difficult to disperse risk of fire is more.

Contents: CNG vs LPG

Closeup of an LPG nozzle using which LPG is being pumped into a car
Closeup of an LPG nozzle using which LPG is being pumped into a car

edit Production

Natural gas is created over hundreds of years deep within the earth. It has to be extracted (pumped to the surface) and cleaned to remove impurities including water to be marketable. The byproducts of natural gas processing are ethane, propane, butane, pentane and higher molecular weight hydrocarbons.

LPG is manufactured during the refining of petroleum (crude oil), or extracted from petroleum or natural gas streams as they emerge from the ground.

edit Cost

CNG is generally cheaper than LPG. However, propane produces over twice the amount of energy than natural gas. So LPG could be more cost effective than natural gas depending upon local prices (which tend to fluctuate).

Here's an NBC news story on how cost effective and convenient CNG is over gasoline:

edit Availability

There is an extensive distribution network for both CNG and LPG. But the retail availability of LPG is more compared to that of CNG. CNG distribution is mainly via pipeline networks that run from natural gas production wells to various distribution centers and finally into residential neighborhoods and commercial areas.

edit Energy Produced

LPG, vaporized and at atmospheric pressure, has a higher calorific value (94 MJ/m3 or 26.1kWh/m3) than natural gas (38 MJ/m3 or 10.6 kWh/m3). This LPG produces more energy than the equivalent amount of natural gas.

edit Safety and Environmental Impact

Although CNG does produce greenhouse gases upon combustion, it is a more environmentally clean alternative to other fossil fuels like gasoline or LPG. CNG is also safer than other fuels in the event of a spill because natural gas, being lighter than air, disperses quickly when released.

edit Substituting LPG for CNG

Because LPG produces more energy than CNG, it cannot simply be substituted for natural gas. Only gases that have the same Wobbe index are interchangeable. For LPG to have the same Wobbe index as CNG, it has to be mixed with air. A 60:40 ratio for LPG:air mixing is common but it depends upon the composition of LPG because LPG itself is a mixture of propane and butane. This mixture of LPG and air to substitute natural gas is called synthetic natural gas (SNG). Use of SNG is common before the CNG distribution network is fully operational.

edit Odorant

Ethanethiol or ethyl mercaptan is commonly added to both LPG and CNG. Mercaptan has a foul, rotten-egg smell that makes it easy to detect gas leaks.

edit Uses

edit CNG

edit LPG

The following video shows how to convert a car to use LPG along with gasoline.

edit Advantages of using CNG and LPG in vehicles

A CNG tank on the trunk of a CNG and gasoline powered Chevy Cavalier
A CNG tank on the trunk of a CNG and gasoline powered Chevy Cavalier

edit CNG

edit LPG

edit Disadvantages of using CNG and LPG in vehicles

edit CNG

CNG occupies more space than gasoline. Additional space in the trunk of a car or the bed of a pickup truck is used to store the CNG tanks. This problem has been mitigated in factory-built CNG vehicles by installing the tanks under the vehicle body, e.g. Fiat Multipla, Fiat Panda, Volkswagen Touran Ecofuel, Volkswagen Caddy Ecofuel, and Chevvy Taxi.

edit LPG

edit References

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Comments: CNG vs LPG

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Anonymous comments (4)

October 18, 2013, 1:38pm

— 12.✗.✗.25

October 18, 2013, 1:51pm

Under the safety section, both gases disperse into the atmosphere quickly with CNG rising and LPG dropping. Unless LPG confined in a pit it would no less safe then CNG. The other safety item left out is that CNG is stored in its vessel at 3,000 plus PSI and LPG is stored in its vessel between 50-180 PSI.

— 12.✗.✗.25

September 12, 2013, 4:30pm

The use of CNG in Delhi has not improved air qualtiy. Infact, the pollution lelvesl are alarming and Delhi is one amongst top pollutinh cities in the world. It is, therefore, necessary to look inot non polluting forms of fuel for the vehilces. Unfortunately, practice oriented researh using solar energy is getting aback seat. There is an urgent need to look into these issues.
Profesor Ashok Deshpande PhD (Environmental Engineering)

— 59.✗.✗.18

February 21, 2014, 1:25am

>Natural gas vehicles have lower maintenance costs when compared with other fossil fuel-powered vehicles.
This is untrue. My car started fire twice because of this modification.

— 190.✗.✗.249


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