Diesel is more expensive than gasoline here in the US (or do you call regular gas "petrol"? hehe). It used to be cheaper, so I'm not sure why the sudden change, unless they're taxing it more because of it's higher particulate emissions.

Diesel is also more expensive here than regular petrol, but it still provides more miles to the tank so it's still the more economical choice, and of course with some minor mods it's possible to run on biodiesel.

Either way we are always shafted for fuel costs. A litre of diesel is now £1.15!