CNG is more eco-friendly than petrol/diesel, since

a. CNG burns more efficiently
b. CNG can be easily delivered through pipelines
c. CNG cannot be adulterated

CNG is a readily available alternative to gasoline that is made by compressing natural gas to less than 1% of its volume at standard atmospheric pressure. It consists mostly of methane. It is odourless, colourless and tasteless. CNG is better than petrol/ diesel because it has very low moisture content, it is cheap, easy to transport, and it burns more efficiently, completely, and cannot be adulterated.

The main problem with switching over to CNG is the difficulty of laying down pipelines to deliver CNG through distribution points/pumps and ensuring uninterrupted supply.