This data is from my February 2011 trip:
Average 10,34MAD/l or 0,91EUR/l
Average 7,10MAD/l or 0,63EUR/l
Average 349MRO/l or 0,87EUR/l
Average 790XOF/l or 1,20EUR/l
Didn't pay attention if it was leaded or not, I was riding a '97 Africa Twin.
In W. Sahara sometimes petrol had a nasty dark color, but the engine kept on going
In my mind it is handy to know the distance between fuel station in W. Sahara and Mauritania, since there are so few. Please PM me if you need their waypoints.