Diesels are superior for gas mileage.
Which are best: petrol car or diesel for new car?
Well ... If you want to have one that's better for the environment ... Diesel. And then run it using biodiesel - recycled cooking oil, etc. Some people even make their own from the waste cooking oil of local restaurants - for less than it would cost to buy from a gas station.
The status and performance of diesel has changed over the years. It is definitely more economical and sometimes even cleaner than you'd expect. But do your figures. A lot of people are still convinced that petrol is better than diesel because of the sound that you get from the car processing the fuel.
