These vehicles are known as CNGs, and can run 'dual fuel' - traditional liquid hydrocarbon & natural gas - making them extremely versatile, and in high demand. Especially in Utah where natural gas prices are the lowest in the nation; just .74 cents per gallon. Plus, emissions are dramatically lower in a CNG vehicle. Couple that with federal tax incentives, and Utahans are 'gassed' about natural gas cars.
Consumers who buy a new vehicle that runs only on natural gas qualify for a $4,000 tax credit. Utah will kick in another $3,000 in tax credits through its own program. The "gotcha" there is that the only vehicle that qualifies is the Honda Civic GX, and in Utah, only Ken Garff Honda downtown sells them, further limiting the supply of qualifying vehicles. The CNG Civic sells for about $25,000. Minus the tax credits, the price is about $130 more than the Civic's gas-engine counterpart.
Tax credits are tied to the vehicle, not the owner, so potential buyers in Utah should check with the Division of Air Quality, which issues tax-credit certificates for CNG vehicles, before buying to see if a particular vehicle is still eligible for the credit.
Check out CNG Motors which specializes in late model used natural gas vehicles. But remember, you may have a hard time finding a filling station