Western Sahara, south part of Marocco, is a low tax area because it's a sort of Spanish ground but occupied by the Moroccans.
Correct me if i am very wrong, i don't know the details anymore.
If you can go to Dakhla harbor you will pay +/- €.0,30 cents per litre. A few years ago i was there by car and i payed €.0,25.
There is often a strong thermical wind
in the bay.