What is compressed natural gas?
Extracted natural gas goes through a long and complicated multi-stage process. In the end, compressed natural gas is only 1% of the volume it occupied before (at standard atmospheric pressure).
Despite being compressed, CNG is still a gaseous product containing methane, nitrogen, CO2, propane, and ethane. Pollutant emissions are low: while burning, CNG produces less CO, hydrocarbons, and nitrogen oxides.

Natural Gas Vehicles
Natural gas powers more than 175,000 vehicles in the United States and roughly 23 million vehicles worldwide. Natural gas vehicles (NGVs) are good choices for high-mileage, centrally fueled fleets because they can provide similar fuel range support for applications that stay within a region supported by reliable compressed natural gas (CNG) fueling. The advantages of natural gas as a transportation fuel include its domestic availability, widespread distribution infrastructure, and reduced greenhouse gas emissions over conventional gasoline and diesel fuels.
The horsepower, acceleration, and cruise speed of NGVs are comparable with those of equivalent, conventionally fueled vehicles. Also, compared with conventional diesel and gasoline vehicles, NGVs offer other air quality benefits beyond greenhouse gas emissions.