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Natural Gas
What is it?
Natural gas is an odorless, gaseous mixture of hydrocarbons—predominantly made up of methane (CH4). It occurs naturally underground and is extracted through gas wells or alongside crude oil production. Stored as Compressed Natural Gas (CNG) or Liquid Natural Gas (LNG), it offers significant cost savings, typically one-third less than gasoline at the pump.
The vast majority of natural gas in the United States is considered a fossil fuel because it is made from sources formed over millions of years by the action of heat and pressure on organic materials.
There are three types of Natural gas made into fuel:
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Compressed Natural Gas (CNG)
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Liquefied Natural Gas (LNG)
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Renewable Natural Gas (RNG)
Renewable Natural Gas (RNG), also known as “biomethane”, is a pipeline-quality vehicle fuel. It is produced by purifying biogas, which is generated through anaerobic digestion of organic materials—such as waste from landfills and livestock—or through thermochemical processes, such as gasification. RNG qualifies as an advanced biofuel under the Renewable Fuel Standard. Because RNG is chemically identical to fossil-derived conventional natural gas, it can use the existing natural gas distribution system. 94% of all on-road fuel in natural gas vehicles in calendar year 2025 was RNG.
What are the Benefits?
Whether produced via conventional or renewable methods, the advantages of natural gas as an alternative fuel include its domestic availability, established distribution network, relatively low cost, and air quality benefits.
Compared to conventional gasoline and diesel, compressed natural gas (CNG) prices are much more stable, protecting your organization from unexpected fuel price spikes and allowing for extended fueling contracts. Natural gas is typically transported to fueling stations via pipeline. This allows for access to fuel in situations that would otherwise strain gasoline or diesel supplies, which are moved by truck. Examples include hurricanes and extreme weather events.
Additionally, natural gas burns cleaner than gasoline and diesel, reducing greenhouse gas emissions for vehicles. The AFDC reports that light-duty vehicles running on conventional natural gas have a lifecycle greenhouse gas reduction of approximately 15% compared to their conventional counterparts. The environmental impact is further reduced if renewable natural gas (RNG) is implemented into the fueling system as opposed to purely conventional sources.
Natural Gas in Maine
Greater Portland METRO
In 2006, Greater Portland METRO became the first transit agency in Maine to adopt compressed natural gas (CNG) buses, introducing 13 CNG buses alongside the state's first CNG fueling station. The project replaced aging diesel buses with cleaner-burning natural gas vehicles, reducing diesel consumption while demonstrating the viability of alternative fuels for public transit in Maine. The fueling station was designed to serve additional fleets, helping lay the foundation for broader CNG adoption across the region.
METRO's investment also enabled a partnership with Portland Public Schools, whose CNG school buses use METRO's fueling station and maintenance facility instead of building separate infrastructure. By sharing resources, the two fleets reduced costs while expanding the use of natural gas vehicles in southern Maine. At its peak, more than 40% of METRO's fleet operated on CNG, displacing approximately 150,000 gallons of diesel fuel each year.
As transit technology has evolved, METRO has begun incorporating battery-electric buses into its fleet while continuing to demonstrate the value of alternative fuels in public transportation. The agency's early investment in CNG provided a model for fleet collaboration and helped establish some of Maine's first alternative fuel infrastructure for heavy-duty vehicles.
Resources
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