Ram estimates the truck will deliver 15% less power and torque in CNG mode. But it expects some fleets will accept less capability so that they can save at the pump. During the show, an area public pump offered CNG for the gasoline-gallon equivalent of $2.15, according to CNGprices.com. Gasoline in the city averaged $3.77, said IndyGasPrices.com.

While relying on aftermarket suppliers, other truck makers are offering CNG as an available dealer option. GM took the wraps off two such trucks: the bifuel 2013 Chevrolet and the GMC Sierra 2500 HD pickup. They have a range of 650 miles on CNG and gasoline combined. GM builds the trucks in Ft. Wayne, Ind., then ships them to a nearby IMPCO Technologies Inc. plant for the CNG upfit. Prices were not disclosed.

Powered by a hardened, 6.0-liter Vortec V-8, GM's bifuel trucks are available in short and long boxes as well as two- and four-wheel drive. CNG does not start easily in a cold engine, so, like the Ram, GM's trucks ignite on gasoline and then switch to CNG automatically. However, if the GM trucks have no gasoline in the tank, they will not start. The Ram will start on CNG if the gas tank is empty.

GM estimates its bifuel trucks will deliver about 12% less power in CNG mode. Its trucks use a composite tank mounted inside a steel enclosure in the bed. The extra weight reduces payload capacity by 450 lb. Powertrain components are covered under a five-year, 100,000-mile warranty. Other parts are covered under a three-year, 36,000-mile warranty. Next month, GM is taking orders for year-end delivery.

Ford showcased a new bifuel system, produced by Westport LD, which can be had on three-quarter and one-ton trucks. The company displayed an F-250 Super Duty pickup with a Westport WiNG power system that uses a tank enclosure in the bed and offers a 600-mile, combined-fuel range. Costing $9,750 more than a conventional F-250 or F-350, the bifuel truck always starts up on CNG, then switches to gasoline for extended range. The truck can operate on CNG in -20° F temperatures, and Westport estimates that power is cut by 5% in CNG mode. The tank adds about 400 lb.

Available for summer delivery, Ford's truck is built in Lousiville, Ky., then a nearby Westport factory provides the CNG upfit. Powered by a hardened, 6.2-liter V-8 that accepts propane, the truck can be ordered in a short- or long-bed configuration in any cab style. The CNG tank has a three-year, 36,000-mile warranty, and other parts are covered under a five-year, 50,000-mile warranty.

The trucks use different methods to tell the driver when the fuels switch. Ram offers twin analog fuel gauges and an LCD display in the main instrument cluster, while Westport has a CNG fuel gauge on Ford's center stack. Westport's blue back-lit display goes dark in gasoline mode. GM has a four-light LED readout on the center stack; each light indicates a quarter tank of CNG. Here, a button allows users to switch between fuels. Ram and Ford do not offer manual overrides.

Despite the challenges, the competition is heating up for CNG, and we expect to see even more options coming down the road soon.