Been talking to my mate about Jags. Economy came up. He worked out that his mate's jag would do 17.5 l/100km, at which point i said that its probably the same in mpg.
Well, being engineers we couldn't leave this question open and worked out where the 2 scales cross. So the answer to the question you never thought of asking is:
16.808965763mpg~16.808965763l/100km
Thats actually quite close to the original guess of 17.5.
So now you know