**Q: I'm close to buying a Hyundai i30 1.6 CRDi. It does 60mpg compared with 45mpg for the 1.6 petrol, so it should save me money on fuel.
However, as the price of diesel is quite a bit higher at the moment, would I be better off with the petrol?
A: The diesel's extra 14.5 miles from every gallon make it cheaper on fuel, even though petrol is cheaper at the pumps.
The diesel costs 700 more to buy, though, so you'll have to do a lot of miles before it works out to be the better deal.
Taking only fuel into consideration, you'll break even at around 39,000 miles at today's fuel prices. Do more than that and diesel will be the cheaper bet in the long run.
Take into account all the other motoring bills, such as tax, insurance, depreciation and servicing, and the diesel edges further ahead.
If you keep the car for three years and sell it with 36,000 miles on the clock (as many people will do), the diesel will save you around 700.
The price of diesel is expected to soar even higher over the next few months, though, so forecourt prices would only need to rise by 2.5p a litre for that 700 saving to be wiped out entirely.
Which one you should go for depends entirely on your mileage. If you do the average 10-12,000 miles a year, it's easy - plump for the petrol. If you do 39,000 miles a year or more, look carefully at the diesel, but keep a keen eye on fuel prices.