Natural Gas compressed with the help of compressors and stored in cascades at high pressure and distributed to automobiles is known as CNG. CNG is a fuel that can be used in place of Petrol, Diesel and liquefied petroleum gas (LPG). CNG combustion produces fewer undesirable greenhouse gases than the existing automotive fuels. In comparison to other fuels, natural gas poses less of a threat in the event of a spill, because it is lighter than air and disperses quickly when released. 

CNG is made by compressing natural gas, which is mainly composed of methane (CH₄), to less than 1% of the volume it occupies at standard atmospheric pressure. It is stored in hard metallic and non-metallic containers called as cascade at a pressure of 200 to 250 Bars (20–25 MPa), usually in cylindrical or spherical shapes.

CNG is used in traditional internal combustion engine-based automobiles that have been modified or in vehicles specifically manufactured for CNG use, either alone (dedicated), with a segregated existing fuel system to extend range (dual fuel) or in conjunction with another fuel such as Petrol (bi-fuel). Natural gas vehicles are increasingly used in all over the world specially in the Asia-Pacific region. In Indian capital of Delhi, and other large cities like Ahmedabad, Mumbai, Pune, Kolkata as well as cities such as Lucknow, Kanpur, Agra, Prayagraj, Varanasi, etc. Its use is also increasing in South America, Europe and North America because of rising Petrol prices. In response to high fuel prices and environmental concerns, CNG is starting to be used also in public transport, pickup trucks, school buses, and trains.

The cost and placement of fuel storage containers is the major barrier to wider/quicker adoption of CNG as a fuel. It is also why municipal government, public transportation vehicles were the most visible early adopters of it, as they can more quickly amortize the money invested in the new (and usually cheaper) fuel. In spite of these circumstances, the number of vehicles in the world using CNG has grown steadily (30 percent per year). Now, as a result of the industry’s steady growth, the cost of such fuel storage cylinders has been brought down to a much more acceptable level. Especially for the CNG Type 1, Type 2, Type 3 and Type 4 cylinders, many countries are able to make reliable and cost-effective cylinders for conversion need.

CNG’s volumetric energy density is estimated at 42 percent of that of liquefied natural gas, because it is not liquefied, and at 25 percent of that of diesel fuel.