They still guzzle gas, just a different kind.

General Motors has announced plans to introduce bi-fuel-capable versions of its full-size pickup trucks that can run on either compressed natural gas (CNG) or gasoline. Sales begin at the end of 2012.

Both Chevrolet Silverado and GMC Sierra models will be available to commercial and fleet buyers, but the company has not yet specified if they will be based on the light or super duty versions of the trucks.

GM currently offers CNG versions of its full-size vans that are powered by 6.0-liter V8 engines, but they are not bi-fuel capable. The conversions are handled by Indiana-based supplier IMPCO Automotive, who will also be responsible for the pickup trucks, but sales are handled directly through GM. Drivers of the pickups will be able to switch between gasoline and CNG power at the press of a button.

A recent study from Pike Research predicts that sales of CNG-powered vehicles in the United States will quadruple by 2016, to 33,000 units annually. Globally, nearly 2 million CNG vehicles are sold each year and that number is expected to rise to 3.2 million by 2016, as well.

The appeal of the fuel is mostly due to its low price. It can be bought for as little as $.78 for the equivalent of a gallon of gasoline in Oklahoma and typically less than $2.00 per gallon equivalent nationwide. While the public refueling infrastructure is currently small – less than 1,000 stations across the U.S. – pumps can be installed at home or anywhere there are natural gas lines, which makes refueling convenient, particularly for fleet operators.

CNG has also found advocates in both the environmental and energy security arenas thanks to its clean-burning nature and largely domestic production. Over 90 percent of natural gas used in the United States is sourced locally.

The bi-fuel design of the GM pickups will allow them to travel to areas where CNG is not available, but if the vans are anything to go by, range should not be an issue as they can go 300 miles between fill ups.

Ford also sells a version of its Transit Connect that is prepped for CNG use, but the buyer must have it converted after sale. The alt-fuel compact vans are quickly gaining popularity among Taxi companies. Startup automaker VPG recently began direct sales of a CNG-powered minivan called the MV-1 that is designed for use by people who use wheelchairs and other assistive equipment.

The only CNG-powered car that is currently on the market is the Honda Civic Natural Gas. Previously available only to fleet buyers in four states, the updated 2012 model is now on sale to retail customers in 35 states for $26,895 before various federal and state tax credits.

GM currently has no plans to introduce a bi-fuel car, at least not in the United States. However, its Dutch customers can pick up a bi-fuel version of the Chevy Spark microcompact for $13,000. The only drawback?

No bed.

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