What is the average price of unleaded petrol on motorways in northern France?
The French Government have an official site where you can check the fuel prices and even work out the total cost of your journey. It’s in French but still fairly easy for a non French-speaker to use. http://www.prix-carburants.gouv.fr/ The motorway filling stations are open al the time but if you take the other poster’s advice and leave the motorway to refuel remember that petrol stations in towns or at supermarkets will be unmanned between the hours of about 12:00 and 14:30 and after about 19:30 and the 24/7 pay-at-pump machines will only accept French credit cards.