Bot is correct the BTU rating for CNG is far lower than gas or diesel. The storage pressures in a CNG converted vehicle are currently 3600psi. a normal cylinder will give about 6 gallons equivalent. dual fuel vehicles are available but none of the current OEM's offer them. Depending on tanks capacity you will get about 65 to 150 miles on CNG system and the current cost to convert a normal gas vehicle is around $30K. The tanks are super expensive. now LPG (propane) is a very viable alt fuel, BTU rating is at or better than gas and diesel and it is stored under much less pressure. Clean Fuels USA offers a system for the medium truck market for about $11K that uses the 8L GM gas V8 and it runs like a spotted ape. the fittings to refuel can be found at any propane company found in any small town. I am currently looking into moving some of our fleet to this since the current cost per gallon of LPG is $2.00.

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Keith Schuster
2006 E350 98K miles
2013 Ford Explorer 15K miles