CNG is made by compressing natural gas (which is mainly composed of methane [CH4]), to less than 1% of its volume at standard atmospheric pressure. It is stored and distributed in hard containers, at a normal pressure of 200–220 bar (2900–3200 psi), usually in cylindrical or spherical shapes.
CNG is used in traditional gasoline internal combustion engine cars that have been converted into bi-fuel vehicles (gasoline/CNG). Natural gas vehicles are increasingly used in Europe and South America due to rising gasoline prices.
In response to high fuel prices and environmental concerns, CNG is starting to be used also in light-duty passenger vehicles and pickup trucks, medium-duty delivery trucks, transit and school buses, and trains.
CNG's energy density is 42% lower than LNG (because it is not liquefied), and 25% lower than diesel.
 TechnologyOtto-cycle (gasoline) and modified Diesel cycle engines. Lean-burn Otto-cycle engines can achieve higher thermal efficiencies when compared with stoichiometric Otto-cycle engines at the expense of higher NOx and hydrocarbon emissions. Electronically-controlled stoichiometric engines offer the lowest emissions across the board and the highest possible power output, especially when combined with exhaust gas recirculation, turbocharging and intercooling, and three-way catalytic converters, but suffer in terms of heat rejection and fuel consumption. A suitably designed natural gas engine may have a higher output compared with a petrol engine because the octane number of natural gas is higher than that of petrol.
CNG may be refueled from low-pressure ("slow-fill") or high-pressure ("fast-fill") systems. The difference lies in the cost of the station vs. the refueling time. There are also some implementations to refuel out of a residential gas line during the night, but this is forbidden in some countries. Fueling a vehicle from a home natural gas fuel line is becoming more popular in the United States, especially in California and New York, and tax credits are available for installing the necessary appliance.
CNG cylinders can be made of steel, aluminum, or plastic. Lightweight composite (fiber-wrapped thin metal "ISO 11439 CNG-3"/fibre-wrapped plastic "ISO 11439 CNG-4") cylinders are especially beneficial for vehicular use because they offer significant weight reductions when compared with earlier generation steel and aluminum cylinders, which leads to lower fuel consumption. The CNG cylinders bundled with safety-valve generally follow the ISO 11439 standard. 
The equipment required for CNG to be delivered to an Otto-cycle engine includes a pressure regulator (a device that converts the natural gas from storage pressure to metering pressure) and a gas mixer or gas injectors (fuel metering devices). Earlier-generation CNG conversion kits featured venturi-type gas mixers that metered fuel using the Venturi effect. Often assisting the gas mixer was a metering valve actuated by a stepper motor relying on feedback from an exhaust gas oxygen sensor. Newer CNG conversion kits feature electronic multi-point gas injection, similar to petrol injection systems found in most of today's cars.
 DrawbacksCompressed natural gas vehicles require a greater amount of space for fuel storage than conventional gasoline power vehicles. Since it is a compressed gas, rather than a liquid like gasoline, CNG takes up more space for each gasoline gallon equivalent (GGE). Therefore, the tanks used to store the CNG usually take up additional space in the trunk of a car or bed of a pickup truck which runs on CNG. This problem is solved in factory-built CNG vehicles that install the tanks under the body of the vehicle, thanks to a more rational disposition of components, leaving the trunk free (eg. Fiat Multipla, New Fiat Panda, Volkswagen Touran Ecofuel,Chevy Taxi (sold in countries such as Peru) etc). While CNG-powered vehicles are considered to be safer than gasoline-powered vehicles , there are concerns about how best to fight fires involving CNG vehicles.
 CNG carsCNG cars available in Europe are actually flexible-fuel vehicles. Their engine is a standard gasoline internal combustion engine (ICE). This means that they can indifferently run on either gasoline from a gasoline tank or CNG from a separate cylinder in the trunk. The driver can select what fuel to burn by simply flipping a switch on the dashboard.
Several manufacturers (Fiat, Opel(General Motors), Peugeot, Volkswagen, opel Zafira 1.6 CNG and others) sell bi-fuel cars.
Almost any existing gasoline car can be turned into a bi-fuel (gasoline/CNG) car. Authorized shops can do the retrofitting, this involves installing the CNG cylinder in the trunk and installing the CNG injection system and electronics. Besides the lower costs, a major benefit is that CNG cars can reduce pollution.
 CNG LocomotivesCNG Locomotives are operated by several railroads, including Ferrocarril Central Andino in Peru, which has run a CNG Locomotive on a freight line since 2005 , and the Napa Valley Wine Train, which replaced its diesel locomotive with a CNG locomotive in May of 2008. CNG locomotives are usually diesel locomotives that have been converted to use compressed natural gas generators instead of diesel generators to generate the electricity that drives the motors of the train. Some CNG locomotives are able to fire their cylinders only when there is a demand for power, which, theoretically, gives them a higher fuel efficiency than conventional diesel engines.
 CNG compared to LNGCNG is often confused with liquefied natural gas (LNG). While both are stored forms of natural gas, the key difference is that CNG is in compressed form, while LNG is in liquefied form. CNG has a lower cost of production and storage compared to LNG as it does not require an expensive cooling process and cryogenic tanks. CNG requires a much larger volume to store the same mass of gasoline or petrol and the use of very high pressures (3000 to 4000 psi, or 205 to 275 bar).
 CanadaCanada is a large producer of natural gas, so it follows that CNG is used in Canada as an economical motor fuel. Canadian industry has developed CNG-fueled truck and bus engines, CNG-fueled transit buses, and light trucks and taxis. Both CNG and propane refueling stations are not difficult to find in major centres.
 United States of AmericaIn the US, federal tax credits are available for buying a new CNG vehicle. Use of CNG varies from state to state. In California, CNG is used extensively in local city and county fleets, as well as public transportation (city/school buses), and there are 90 public fueling stations in Southern California alone. Although natural gas prices are rising, compressed natural gas is available at 30-60% less than the cost of gasoline, as a rule of thumb, in much of California. Personal use of CNG is a small niche market currently, though with current tax incentives and a growing number of public fueling stations available, it is experiencing unprecedented growth. The state of Utah offers a subsidised statewide network of CNG filling stations at a rate of $0.85/gge, while gasoline is above $4.00/gal. Elsewhere in the nation, retail prices average around $2.50/gge, with home refueling units compressing gas from residential gas lines for approx $1.50/gge. Other than aftermarket conversions, and government used vehicle auctions, the only currently produced CNG vehicle in the US is the Honda Civic GX sedan, which is made in limited numbers and available only in a few states. An initiative, known as Pickens Plan, calls for the expansion of the use of CNG as a standard fuel for cars has been recently started by oilman and entrepreneur T. Boone Pickens.
Congress has encouraged conversion of cars to CNG with a tax credits of up to 50% of the auto conversion cost and the CNG home filling station cost. However, while CNG is much cleaner fuel, the conversion requires a type certificate from the EPA. Meeting the requirements of a type certificate can cost up to $50,000.
 EuropeItaly currently has the largest number of CNG vehicles in Europe and is the 4th country in the world for number of CNG-powered vehicles in circulation.
The use of methane (CNG) for vehicles started in the 1930's and has continued off and on until today.
Currently (06/2008) there is a large market expansion for natural gas vehicles (CNG and LPG) caused by the rise of gasoline prices and by the need to reduce air pollution emissions.
Before 1995 the only way to have a CNG-powered car was by having the retrofitted with an after-market kit. A large producer was Landi Renzo, Tartarini Auto, Prins Autogassystemen, OMVL, BiGAs,... and AeB for electronic parts used by the most part of kit producer.
Landi Renzo and Tartarini have divisions selling vehicles in Asia and South America.
After 1995 bi-fuel (gasoline/CNG)cars became available from several major manufacturers. Currently Fiat, Opel(GM), Volkswagen, Citroen, Renault, Volvo and Mercedes sell various car models and small trucks that are gasoline/CNG powered. Usually CNG parts used by major car manufacturers are actually produced by after-market kit manufacturers, e.g. Fiat use Tartarini Auto components, Volkswagen use Teleflex GFI and Landi Renzo components.
In Italy, there are more than 800 CNG stations .
In Germany, CNG-generated vehicles are expected to increase to two million units of motor-transport by the year 2020. The cost for CNG fuel is between 1/3 and 1/2 compared to other fossil fuels in Europe. in 2008 there are around 800 gas(CNG) stations in Germany
In Portugal there are 4 CNG refueling stations but 3 of them do not sell to the public. Only in Braga you can find it on the local city bus station (TUB).
 South AmericaArgentina and Brazil are the two countries with the largest fleets of CNG vehicles. Conversion has been facilitated by a substantial price differential with liquid fuels, locally-produced conversion equipment and a growing CNG-delivery infrastructure. A 'Blue-network' of CNG stations is being developed on the major highways of the Southern Cone (including Chile and Bolivia) to allow for long-haul transportation fuelled by CNG......
CNG has grown into one of the major fuel sources used in car engines in Iran, Pakistan, Bangladesh and India. The use of CNG is mandated for the public transport system of India's capital New Delhi as well as for the city of Ahmedabad in the state of Gujarat. The Delhi Transport Corporation operates the world's largest fleet of CNG buses. The government of Punjab, Pakistan, the most populous province of that country, has mandated that all public-transport vehicles will use CNG by 2007. Today many rickshaws as well as personal vehicles in India and Bangladesh are being converted to CNG powered technology, the cost of which is in the range of $800-$1000. In the Bangladesh capital of Dhaka not a single auto rickshaw without CNG has been permitted since 2003. As of July 2007 Pakistan is the largest user of CNG in Asia, and second largest user in the world.
According to the International Association for Natural Gas Vehicles, Pakistan has the second-largest number of natural gas vehicles. Recently Landi Renzo of Italy has set up a production subsidiary in Karachi to cater to the growing demand of CNG Kits in Pakistan. OEM's like Toyota Pakistan and Suzuki Pakistan is producing company fitted CNG cars.
In the Middle East and Africa, Egypt is a top ten country in the world with more than 63000 CNG vehicles and 95 fueling stations nationwide. Egypt was also the first nation in Africa and the Middle East to open a public CNG fueling station in January 1996.
In Singapore CNG is increasingly being used by public transport vehicles like buses and taxis, as well as goods vehicles. However, according to Channel NewsAsia on April 18, 2008, more owners of private cars in this country are converting their petrol-driven vehicles to also run on CNG - motivated no doubt by fiercely-escalating petrol prices these days. The initial cost of converting a regular car to bi-fuel at the German conversion workshop of C. Melchers-Galileo, for example, is around S$4,000 (US$2,300); with the promise of real cost-savings bi-fuel cars bring in the long term.
Singapore currently has three operating filling stations for natural gas. SembCorp Gas Pte Ltd runs the station on Jurong Island, and jointly with Singapore Petroleum Company, the filling station at Jalan Buroh. Both these stations are in the western part of the country. Another station on the mainland is in Mandai Link to the north and is operated by SMART Energy. SMART also plans a second station on Serangoon North Ave 5 which will be set up the 2nd half of 2008; so will two more - at Jalan Bukit Merah and Bedok in the central and eastern parts of the country.
As a key incentive for using this eco-friendly fuel Singapore has a Green Vehicle Rebate (GVR) for users of CNG technology. First introduced in January 2001, the GVR grants a 40% discount on the Open Market Value (OMV) cost of newly-registered green passenger vehicles.
In Malaysia, the use of CNG was originally introduced for taxicabs and airport limousines during the late-1990s, when new taxis were launched with CNG engines while taxicab operators were encouraged to send in existing taxis for full engine conversions; any vehicle converted to use CNG is labelled with white rhombus "NGV" (Natural Gas Vehicle) tags, lending to the common use of "NGV" when referring to road vehicles with CNG engine. The practice of using CNG remained largely confined to taxicabs predominantly in the Klang Valley due to a lack of interest. No incentives were offered for those besides taxicab owners to use CNG engines, while government subsidies on petrol and diesel made conventional road vehicles cheaper to use in the eyes of the consumers. Petronas, Malaysia's state-owned oil company, also monopolises the provision of CNG to road users. As of July 2008, Petronas only operates about 150 CNG refueling stations, most of which are concentrated in the Klang Valley. At the same time, another 50 was expected by the end of 2008.
As fuel subsidies were gradually removed in Malaysia starting June 5, 2008, the subsequent 41% price hike on petrol and diesel led to a 500% growth in the number of new CNG tanks installed. National car maker Proton considered fitting its Waja, Saga and Persona models with CNG kits from Prins Autogassystemen by the end of 2008, while a local distributor of locally assembled Hyundai cars offers new models with CNG kits. Conversion centres, which also benefited from the rush for lower running costs, also perform partial conversions to existing road vehicles, allowing them to run on both petrol or diesel and CNG with a cost varying between RM3,500 to RM5,000 for passenger cars.
 OceaniaDuring the 1970s and 1980s, CNG was commonly used in New Zealand in the wake of the oil crises, but fell into decline after petrol prices receded.
Brisbane Transport and Transperth in Australia have both adopted a policy of only purchasing CNG buses in future. Transperth is purchasing 451 Mercedes-Benz OC500LE buses and is undertaking trials with articulated CNG buses from Scania, MAN, and Irisbus, while Brisbane Transport has purchased 216 Scania L94UB and 240 MAN 18.310 models as well as 30 MAN NG 313 articulated CNG buses. The State Transit Authority of New South Wales (operating under the name "Sydney Buses") operates 102 Scania L113CRB buses, two Mercedes-Benz O405 buses and 300 Mercedes-Benz O405NH buses and are now taking delivery of 255 Euro 5-compliant Mercedes-Benz OC500LEs.
In the 1990s Benders Busways of Geelong, Victoria trialled CNG buses for the Energy Research and Development Corporation.
Martin Ferguson, Ollie Clark, and Noel Childs featured on ABC 7.30 Report raising the issue of CNG as an overlooked transport fuel option in Australia, highlighting the large volumes of LNG currently being exported from the North West Shelf in light of the cost of importing crude oil to Australia. The opportunity and pathways to industry development are mapped out in summary on the Rosetta Moon news site.
 See also
- ^ http://www.envocare.co.uk/lpg_lng_cng.htm
- ^ ISO 11439: Gas cylinders -- High pressure cylinders for the on-board storage of natural gas as a fuel for automotive vehicles
- ^ "How Safe are Natural Gas Vehicles?". Clean Vehicle Education Foundation. Retrieved on 2008-05-08.
- ^ "How Safe is Natural Gas?". Retrieved on 2008-05-08.
- ^ "Fighting CNG fires". Retrieved on 2008-05-08.
- ^ "The First CNG Train Starts Functioning in Peru - Paula Alvarado - June 21, 2005". Retrieved on 2008-08-20.
- ^ "Napa Valley Wine Train Tests CNG Locomotive - Tech.Winetrain - May 15, 2008". Retrieved on 2008-08-20.
- ^ "Natural Gas Prices in the US". Retrieved on 2008-06-07.
- ^ a b "NGV Statistics". International Association for Natural Gas Vehicles. Retrieved on 2007-11-14.
- ^ Allen, Robin (1999-05-11). "New fuel cleans up: CNG: Compressed natural gas is rapidly gaining popularity with drivers; Surveys edition", Financial Times, p. 17.
- ^ "More natural gas stations needed, say motorists". The Star Online (2008-06-13). Retrieved on 2008-08-04.
- ^ a b Rashvinjeet S. Bedi (2008-06-08). "Motorists rush to check out NGV system". The Star Online. Retrieved on 2008-08-04.
- ^ Vinesh, Derrick (2008-06-25). "Long queue for NGV kits". The Star Online. Retrieved on 2008-08-04.
- ^ "Proton cars to come with NGV kits". The Star Online (2008-06-28). Retrieved on 2008-08-04.
- ^ Elaine Ang and Leong Hung Yee (2008-07-07). "Moving towards hybrid vehicles". The Star Online. Retrieved on 2008-08-04.
- ^ Perumal, Elan (2008-06-13). "Rush to fit natural gas gadget". The Star Online. Retrieved on 2008-08-04.
- ^ "NGV Bus Demonstration - H Bender - December 1993". Retrieved on 2007-07-26.