GM's is converting heavy duty pickups to run on compressed natural gas for $9,500, adding to their CNG-capable fleet that already includes their van lineup and soon the Impala sedan.

The Chevrolet and GMC vehicles are setup to be "bi-fuel capable," meaning they can still run on gasoline when CNG is unavailable. GM's conversions are covered by a five-year, 100,000 mile warranty. See the details on the CNG Silverados and Sierras .

Ram has been selling CNG-capable 2500 trucks for a few years already, and currently offers the kit on their Tradesman and SLT trucks running 5.7 HEMI V8 engines. However they're pretty elusive on price... I could only find third-party figures on the previous model.

Ford doesn't offer an OEM CNG conversion, but they do make the changeover available to heavy duty truck buyers through their network of Approved Modifiers. Ford honors their own engine and powertrain warranty for five years or 60,000 miles if a conversion is performed through one of their approved affiliates, and expects the modifier to supply the CNG system component warranty.

One of the more popular Ford modifiers is Westport Wing, who offer an F-250 bi-fuel system for $9,750 for the basic system with an 18.5-gallon tank and $10,950 for a 24-gallon setup. However, there are other approved shops out there who do it for less.

Chevy's CNG conversion can be fitted to all 2500 and 3500 single rear-wheel pickups (a name that's misleading... these aren't Morgan-style trucks, that's just what the industry calls "not duallys"). A Work Truck-trim Silverado 2500 RWD with a long box and regular cap, the cheapest Chevy HD pickup at an MSRP of $32,405, could be yours running natural gas for a total of around $43,000.

Meanwhile, the price of natural gas is running a huge range at between 15% and 60% cheaper than gasoline depending on where you're buying it.

Do you think GM's conversion is going to be a winning proposition for fleets and commercial truck operators, or are the savings too uncertain to justify the investment?