Diesel is actually cheaper to produce than Petrol because it requires less processing, and is the 1'st off take in the "distillation or refining process". It used to be cheaper than petrol until about 2003 or 2004. I think the argument for it being more expensive until recently was that it's cost of production is greater than petrol (additional costs to cater for low sulphur diesel, but a mate of mine in the industry reckons even that excuse is a load of bollocks because all they need to do is blend low sulphur oil with higher sulpur oil to obtain the required sulhpur levels).
