Compressed natural gas requires a higher upfront cost for the vehicle, primarily for the tank. A tank for a CNG Honda Civic costs about $5,000. The price tag on a heavy-duty truck is much higher, roughly $40,000, or about 20% or 50% more than the price of a conventional rig.

"We want to fund research that will fund innovative tanks," Chu told conferees.

"[We will see] less expensive compressed air tanks, or even better, the tank will have absorbent material inside so that you can have the same amount of natural gas at a much lower pressure. If we can solve this hurdle, then natural gas can be an alternative to gasoline or diesel."

Unlike car owners, fleets are comparing such investments to their long-term operating costs, and some are already reaping savings.

Earlier this year, ">ENR reviewed a concrete mixer that ran on compressed natural gas. At the filling station, we observed a 28% reduction in fueling costs without any noticeable loss in performance.

General Motors Co. and Chrysler Group LLC are showing new ">natural-gas pickups at this year's Work Truck Show. Ford Motor Co. offers prep kits for its commercial line, as well.

"Conservatively, in four years, it pays for itself if you hang onto these trucks for 10 years, and if the price drops more where we think it will be, then [the payback is] perhaps two years or less," Chu said. "This is a no-brainer."