Still fossil fuel, but better than gasoline and diesel...As much as we can wish that everybody would walk, bike, take transit, or drive plug-in hybrids and electric cars, there's a need out there for big pickup trucks, and it might take a while longer before there are good electric or plug-in hybrid options. Yet if our goal is to reduce carbon emissions and improve air quality, trucks are a low-hanging fruit. Because they burn a lot more fuel than smaller vehicles, and because they are often used for work by contractors and such who drive them more than the average commuter, there are big gains to be made by making them more efficient and cleaner.
In other words, with everything else being equal, if you have the choice between making a compact car or a big pickup truck 50% more efficient, you should always pick the truck because while the relative improvement is the same, the absolute number of fuel saved will be much higher with the truck.
The 2014 Ford F-150 with 3.7-liter V6 engine will be available this fall with a factory-installed, gaseous-fuel prep package that includes hardened valves, valve seats, pistons and rings so it can operate on either natural gas or gasoline through separate fuel systems.
When the 3.7-liter V6 F-150 is equipped with a CNG/LPG engine package, it is capable of achieving more than 750 miles on one tank of gas, depending on the tank size selected. The Ford F-150 averages 23 mpg on the highway.
When it comes to emissions, the biggest benefit is for smog-forming emissions. Natural gas simply burns cleaner than gasoline and (especially) diesel. But carbon emission benefits, while real, are a bit more marginal, especially if the whole life-cycle of the fuel is taken into account.
According to the U.S. Department of Energy, CNG emits approximately "6% to 11% lower levels of GHGs than gasoline throughout the fuel life cycle". But bigger benefits can be achieved if we capture gas that would otherwise be flared (ie. wasted) and do something useful with it, or if we use biogas from sources that would otherwise release methane in the atmosphere (ie. landfill capture systems).
Bottom line, CNG is still dirty, but while we wait for better options (ie. fully electric trucks), it can be an improvement over what we have now (especially if it replaces dirtier diesel).
Another benefit is that CNG can be cheaper to operate:
CNG conversions can provide stability against fluctuating fuel prices as well as lower vehicle operating costs for fleet administrators. CNG sells for an average of $2.11 per gallon of gasoline equivalent, and is as low as $1 in some parts of the country, representing a significant savings over unleaded regular fuel. The national average for unleaded regular fuel is $3.66 per gallon.