As used in: Virtually every current car that doesn't use unleaded.
What is it? Like petrol, diesel is distilled from crude oil and burned in an internal combustion engine.
Where can I buy it? Available nationwide at every petrol station.
Pros: Diesel is easy to buy and generally gives better fuel economy and lower carbon dioxide emissions than petrol.
Cons: It has relatively high emissions of tiny particulates, which are linked with breathing difficulties and local pollution. The fuel itself has a finite supply, while diesel cars also have a price premium over petrol cars and are taxed at a higher rate for company car drivers.
Expert view: Diesel engines have been the success story of the past decade. They are more polluting than petrol engines in many respects, although particulate filters and catalytic converters are addressing this. Future diesel/electric hybrids will provide top economy.
Outlook: Diesel technology will improve further, especially with hybrids. However, diesel cannot be considered as a long-term solution.