By JEFF BENNETT

U.S. auto makers are introducing pickup trucks powered by natural gas as they look to catch the growing wave of interest in the fuel as an alternative to gasoline.

On Tuesday, Chrysler Group LLC plans to disclose it will build the first production-line pickup truck powered by natural gas. The auto maker is promising to build at least 2,000 heavy-duty Ram bi-fuel trucks that run on a combination of compressed natural gas and gasoline starting in June.

General Motors Co. on Monday plans to disclose it will offer bi-fuel Chevrolet Silverado and GMC Sierra 2500 pickups in the fourth quarter. The trucks will be built by GM and sent to a supplier that will retrofit them to use compressed natural-gas tanks.

In 2009, the American Gas Association and America’s Natural Gas Alliance met with a variety of auto makers to urge them to build complete CNG-powered pickups at the factory.

Chrysler, which was put under the management control of Italian auto maker Fiat SpA in 2009, took on the challenge.

“As a result of our partnership with Fiat, we are able to get to market with this as quickly as we have to start testing to see the future of this CNG technology,” said Chrysler Ram chief Fred Diaz. Chrysler will sell the Ram 2500 pickups to fleet operators or natural-gas explorers.

Houston natural-gas explorer Apache Corp. has been prodding auto makers to build CNG vehicles for years. Since 2009, the company has converted a quarter of its 1,000 U.S. vehicle fleet to CNG, and expects to increase that to 80%. Chief executive Steven Farris drives a Chevy Avalanche that was retrofitted to run on CNG.

The company’s 250 natural-gas powered vehicles were retrofitted at dealerships, however, raising costs and complexity. Auto makers’ decision to build CNG vehicles on the factory floor helps Apache by providing a single source of truck supply and parts. And it helps position natural gas as a vehicle fuel supported in the mass market, said Frank Chapel, Apache’s director of natural gas transportation fuels. “It shows [auto makers] think they can do this and actually get a payback,” Mr. Chapel said.

Honda Motor Co. has been selling its CNG-powered Civic NG passenger car in the U.S. since 1998. The car, which runs only on natural gas, is distributed by 200 dealers in 36 states with a starting price of about $26,200.

Chrysler said its CNG-powered Rams can travel 255 miles on the fuel before automatically switching to an eight-gallon gasoline tank for an additional 112 miles. GM’s pickups would go up to 650 miles using both CNG and gasoline.

The biggest hurdle to wider use is refueling. Today there are fewer than 400 public CNG fueling stations in the U.S.

The interest in natural-gas vehicles comes as gasoline prices are on the rise again and support for using domestic natural gas to replace oil is gaining support. After years of promoting electric cars, President Obama signaled a change in the administration when he said during his January State of the Union speech the nation needs to explore all alternative energy sources.

“We have a supply of natural gas that can last America nearly 100 years,” Mr. Obama said in his speech. “My administration will take every possible action to safely develop this energy. Experts believe this will support more than 600,000 jobs by the end of the decade.”

Chrysler said its CNG Rams will be built at a Saltillo, Mexico, pickup plant and outfitted with two tanks that sit in the forward position of the 8-foot pickup bed. Inside, the dashboard has two fuel gauges with one displaying a fuel pump over the initials CNG.

“For us, this is the first step and if the opportunity presents itself we wouldn’t turn our back on a CNG-powered passenger car,” said Peter Grady, Chrysler’s vice president of network development and fleet. “We aren’t working on it now but we do have it in the back of our minds.”

GM will build its pickups in Fort Wayne, Ind., and send them to Impco Automotive in Union City, Ind., for installation of the CNG delivery and storage system. The company will take orders in April and start production in the fourth quarter.

Ford Motor Co. has been offering CNG prep kits for about a half-dozen vehicles, including the Transit Connect, since 2009. It will expand the offering to its large Ford 650 pickup truck in the third quarter.

Ford modifies the engines in the vehicles at the factories to operate on CNG and then allows the customer to choose how and where they are fitted with the storage tanks.

Rob Stevens, Ford’s chief engineer for commercial trucks, said the approach allows the company to offer the CNG option across more vehicles. It will switch to factory-built CNG vehicles once demand increases, he said.

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