Now $120
Here are the advnatages, from GM's website:
CNG AND DUAL FUEL VEHICLES
Thanks to the high hydrogen and low carbon content of natural gas, fewer emissions are produced compared to gasoline or diesel engines:
Carbon monoxide (CO) emissions drop 50-75 percent
CO2 emissions are only 144g/km (MVEG)
Hydrocarbons (HC) drop by up to 80 percent
Nitrogen oxide (NOx) emissions are also significantly lower than with gasoline or diesel, and help to lessen the risk of ozone build-up at ground level.