Comparing Costs: CNG vs. Conventional Gasoline

Natural Gas as Auto Fuel

Compressed Natural Gas (CNG) vehicles—sometimes called Natural Gas Vehicles (NGVs)—yield fuel cost and economic savings when compared to any other vehicle, including a hybrid.

  • Gallon of gasoline equivalent or GGE: Since CNG is normally sold as a gas rather than a liquid, it isn’t measured in gallons, but can be converted on an energy basis that equals a gallon of gasoline.

In early 2008, the average price of CNG in the United States was less than $1.00 per GGE, while gasoline has gone through the roof. While CNG maintains a decided price-per-gallon advantage, CNG vehicles have lower fuel efficiency than hybrid vehicles. A Civic GX, for example, averages 32 mpg, while a Prius or Civic Hybrid is rated above 40 mpg. So while a GGE of CNG is cheaper, the Civic GX needs more fuel to operate, and therefore erases some—but not all—of the economic benefits of CNG.

> Read an overview of CNG vehicles as an auto fuel

Where to Fill Up?

There’s a major difference between filling up a gasoline hybrid and a CNG vehicle. Compressed natural gas (pressurized at either 3,000 or 3,600 psi) is available through a network of almost 750 stations in the United States. However, nearly a quarter of these stations are in California, so CNG vehicle owners in other states have fewer fueling options. In addition, many CNG stations sell only to pre-approved customers and have limited operating hours, a major change for customers who are used to purchasing gasoline 24-7.

CNG does offer one option that gasoline does not: the ability to fuel in your own garage, as long as your home has an existing natural gas line. Honda now offers a home refueling unit to buyers of the Civic GX that fills the vehicle at a rate of roughly .4 GGE per hour. This means if the vehicle is parked overnight for 12 hours, it can be replenished with 5 GGE of CNG, enough fuel for a 160 mile round-trip commute. Manufactured by FuelMaker, the unit (called Phill) must be professionally installed inside or outside a home garage. The unit is priced between $3,000 and $4,000, although Honda previously has offered free 4-year leases of refueling units to customers in Southern California.

Honda claims that with a home refueling unit installed, the cost of CNG fill-ups can be as much as 65 percent less than the cost of gasoline. Given the increasing cost of natural gas during the past few years, this claim seems a bit optimistic. At this year’s average residential prices for natural gas, a GGE would cost $1.84, about 17 percent less than a gallon of gasoline. Of course, savings could be higher for owners in states like Michigan or Colorado where natural gas is substantially cheaper than the national average.

The Need to Plan Ahead

The option of home refueling does free the CNG vehicle owner from visiting the gas station. However, travel away from home will require mapping out a network of CNG stations, particularly since the range of NGVs tends to be lower than their gasoline or hybrid counterparts. The Civic GX, for example, stores 8 GGE at 3600 psi, giving the vehicle a maximum range of 312 miles. This is in contrast with the Civic Hybrid, which theoretically can manage 627 miles from the 12.3 gallons of gasoline it its tank. The reduced range results mainly from the difficulty of storing the pressurized fuel on board the vehicle. While a bigger tank could be used, the existing tank in the Civic GX already intrudes into the vehicle’s trunk, reducing cargo room by about 40 percent.


  • Mike

    Nice site on an important issue. Thank you.

    If we were to switch the majority of our electrical power production to nuclear fission, and add more capacity, we could use the off peak capacity to create hydrogen for the next generation vehicles, and power plug-in hybrids. That would also free up large amounts of natural gas now used to produce electricity. That natural gas could be used to power retrofitted vehicles from the existing fleet. Trust me, if natural gas became much cheaper than gas and diesel, many local truck fleets, for example, would jump at converting.

    Hmmm, big reduction in greenhouse emissions, nobody fighting and dying for oil, a distinct loss of income to terrorist states… sign me up!

    Where are our environmental and political leaders???? Too invested in the major oil companies? Or too invested in keeping the global warming crisis going – the one they created when they villified nuculear power?

  • Todd

    Thanks for the thoughts about CNG cars. You mentioned that you have to plan your fill ups in advance. I’ll admit I’m flogging my own site, but I set up a site called cngprices.com that lists CNG stations, their current price (when known), and also tries to list stations that aren’t working. This makes trip planning a whole lot easier for those using CNG.