Another consideration if you are in Italy driving along the Adriatic coast is a diversion via the Republic of San Marino. Fuel is somewhat cheaper here than in Italy (about 6c). From the Rimini south junction on the A14 autostrada, it is approximately 14k to a San Marino petrol station (Serravalle). That will cost you about €3.50 in fuel to get there and back; however, if you have an empty tank larger than 40 liters it is worth it. The city of San Marino is well worth visiting; there are free car parks at the base of the mountain and a cable car to the city.
Petrol is quite expensive in Italy; diesel is somewhat lower in price. Gas [metane] is very cheap but the car conversion is quite expensive. As usual, prices on the autostrada are more expensive than most other stazione di servizio. Italy does not compare well to neighbouring countries. There is a list below, correct at 8-10 March 2016.
Thus, if you are driving to Italy from northern Europe, a diversion to Luxembourg is well worthwhile. You should be prepared to queue for 30 minutes before you reach a pump in the summer! One useful tip, providing you have a good map, is to miss the first petrol station in Luxembourg if on the motorway - petrol at the next is the same price and the queues are far shorter. Don't forget to stock up with cheap alcohol and tobacco if you wish. If your car has a big tank or if you drive slower, you can easily make Austria and refill there!
The route through the Brenner pass into Italy also has an advantage in a much lower charge when compared to the Mont Blanc tunnel [about a quarter of the price]. The disadvantage is the slower passage of the Austrian Fern Pass, being single carriageway; while Austria does not have toll barriers on their motorways, you need to stop at the first service station and buy a toll sticker (8.70 euro) and stick it on your windscreen or face a 200 euro fine if caught by the frequent police patrols. The route through France might be a little faster but is far more costly if you use the French motorways.
UK drivers should note that the strong Pound is reducing the difference in fuel prices; in 2007 it was considerably advantageous to fill up in Europe, but these days you need to be more selective. For UK-based diesel drivers, it is still far less expensive to fill your tank anywhere in Europe, even in Italy!
Country (prices at 8-10 March 2016)
£1.089-1.279 = €1.40-1.64
£1.027-1.159 = €1.32-1.48