The advantages and disadvantages of petrol versus diesel apply to used cars as well as new cars, with diesels generally offering better fuel consumption, while a petrol will offer better refinement and cheaper fuel at the pumps. Another factor that applies to older diesel cars are diesel particulate filters, which can become clogged and cause issues with an absence of longer journeys preventing the DPF from regenerating. If you do not cover an average or above average mileage each year and take a lot of short journeys, a petrol might be a safer option.