Another factor which works against CNG is its higher nitrogen oxide emission levels. Methane, a primary constituent of CNG, contributes to global warming even more than carbon dioxide.

Industry sees bio-diesel and hydrogen as long-term solutions but is baffled by the government’s inaction. So far the jatropha plantation policy has not been finalised even as the government has put ethanol petrol mix norms on the fast track. ‘‘The government’s thrust on blends—ethanol petrol, hydrogen-CNG or bio diesel-diesel—will only delay the exhaustion of fossil fuel,’’ said an IOC official.

However, there is a section that believes CNG is the way to go. ‘‘Availability and price prove that CNG is viable under the current circumstances. There is no straight answer whether subsidies will be there or not but it is viable for cars, buses and three-wheelers with limited operation across the country,’’ said Ashok Leyland Managing Director R Seshasayee.

In fact, the spate of CNG variants set to make an entry in the market suggests industry is reconciled. ‘‘Hydrogen fuel will take some time to develop and the conditions are not conducive for its use. CNG provides the best alternative,’’ said Hyundai Vice President Marketing and Sales Arvind Saxena.

With public transport in Delhi totally powered by CNG, history has been created. But doubts remain on whether it will ever be able to make a national debut.