Fuel efficiency is a form of thermal efficiency that converts chemical potential energy contained in a carrier fuel into kinetic energy. Overall fuel efficiency may vary per device. Non-transportation applications, such as industry, benefit from increased fuel efficiency.

The fuel efficiency of vehicles can be expressed in two ways: Fuel Consumption (The amount of fuel used per unit distance) and Fuel Economy (The distance travelled per unit volume of fuel used).
More fuel efficient cars are manufactured without sacrificing performance and made available on the market.
With new engine technology and plenty of innovations, diesel cars are no longer unwieldy and are as trouble-free and maintenance-free as their petrol versions. Generally, there is a price difference of around Rs 100,000 between petrol and diesel cars. There are primarily two reasons why diesel cars are popular in India. Running cost per kilometer is less and diesel will always be cheaper than petrol.

New technologies are helping smaller engines and so many cars will be getting smaller engines. Engineers throughout the automotive industry are at work making smaller engines behave like bigger ones.