Compressed Natural Gas (CNG) as a Transportation Fuel

What is CNG?

Compressed natural gas, or CNG, is natural gas under pressure which remains clear, odorless, and non-corrosive. Although vehicles can use natural gas as either a liquid or a gas, most vehicles use the gaseous form compressed to pressures above 3,100 pounds per square inch.


How is natural gas produced?

Most natural gas comes from three types of wells: natural gas-and-condensate wells, oil wells, and coal bed methane wells. In 2003, California had over 1,200 natural gas-and-condensate wells operating. Well-extracted natural gas requires a cleanup process before it can be used in vehicles or residences.


Where does natural gas come from?

More than 99 percent of the natural gas used in the United States comes from domestic or other North American sources. However, increasing demand for natural gas in power plants will require new supplies from non-North American countries, increasing our dependence on foreign sources of energy. The Energy Information Administration (EIA) predicts that, by 2025, more than 15 percent of our natural gas supplies will be imported from countries other than Canada and Mexico.


How is natural gas delivered to transportation customers in California?

In 2004, California produced 15.4 percent of its natural gas from in-state wells. The rest is imported by pipeline from Canada and the Rocky Mountain and Southwestern states. California gas utilities such as Pacific Gas and Electric, Southern California Gas, and San Diego Gas & Electric distribute the fuel to customers. Most CNG vehicle fueling stations are owned and operated by private companies and local governments.


How is natural gas stored?

In smaller fueling locations and on vehicles, CNG is stored in thick-walled steel, aluminum, or composite tanks built to last more than 20 years.

Washington Gas new facility in Springfield, VA

Photo: Margaret Smith / DOE, NREL 28005

Is natural gas flammable?

When released, compressed natural gas will mix with air and become flammable only when the mixture is within 5 to 15 percent natural gas. When the mixture is less than 5 percent natural gas, it doesn't burn. When the mixture is more than 15 percent natural gas, there is not enough oxygen to allow it to burn. Because natural gas is lighter than air, it quickly dissipates when released from tanks.


What are the benefits of using natural gas in transportation?

Natural gas is produced both worldwide and domestically at relatively low cost and is cleaner burning than gasoline or diesel fuel. Natural gas vehicles show an average reduction in ozone-forming emissions of 80 percent compared to gasoline vehicles.


CNG Vehicle

Photo: Western Washington Clean Cities, NREL 19681

What vehicles use natural gas?

CNG vehicles have been introduced in a wide variety of commercial applications, from light-duty trucks and sedans - like taxi cabs, to medium-duty trucks - like UPS delivery vans and postal vehicles, to heavy-duty vehicles like transit buses, street sweepers (pictured right) and school buses. In California, transit agency buses are some of the most visible CNG vehicles.


Can CNG vehicles access HOV lanes?

California allows single-occupant use of High Occupancy Vehicle (HOV) lanes by CNG vehicles under 14,000 pounds. Owners of eligible vehicles must first obtain an identification sticker from the California Department of Motor Vehicles before using HOV lanes.


Where is CNG fuel available in California?

With the consumption of CNG increasing nationwide 145 percent over the past six years, the fueling infra-structure for natural gas vehicles continues to grow. In 2005, California has more than 200 CNG fueling stations. In Southern California alone, there are more than 100 public fueling stations in major metropolitan areas from Los Angeles to the Mexican border. Another 50 stations are now under construction.

Link to The California NGV Coalition’s 2013 Natural Gas Fueling Station Directory.


Are there any home refueling options for CNG?

A home refueling appliance named "Phill" has been released in California in 2005 from FuelMaker Corporation. With this device, CNG vehicle owners can now refuel their vehicles overnight in their own home, from their household natural gas line. For more information on this appliance, visit the FuelMaker Web Site at www.myphill.com


How much does CNG cost?

Southern California Gas estimates CNG currently costs about 40 percent less than gasoline. As of July 2005, PG&E charges approximately $1.40 per therm, equivalent to about $1.78 per gasoline gallon, for CNG used as a motor fuel.


What types of CNG vehicle projects has the California Energy Commission funded?

The Energy Commission has provided more than $4 million in grant cost-share funding for about 40 CNG fueling stations, the incremental cost of light-duty vehicles, and purchase of 369 CNG-powered school buses. The Energy Commission has also funded research and development to improve the performance of natural gas engines.