Petrol or diesel - which is better?
Both fuels have their disadvantages. The greenest way to travel is by bike, foot or public transport.
Only use your car when it's absolutely essential and consider buying a hybrid.
Petrol engines are less efficient than diesel engines. They emit more carbon dioxide, carbon monoxide and hydrocarbons.
Diesel engines produce more nitrogen oxides, sulphur dioxide, black smoke and particles - associated with poor urban air quality.
Petrol and diesel can be reformulated to cut emissions, e.g. City Diesel / Petrol. A catalytic converter can cut emissions from both.
The ETA's website gives advice on buying greener cars.