Just depends as others have said, on driving style, distances.
My weekly work journey is about 15 miles each way, and different mpg each time, sometimes high 20's others early 30's.
Other evening I went on a 30 minute drive and was seeing 41mpg (had to look twice, and again!).
Preferable to run Super as Nasir says, I use Tesco 99 tends to give the best results personally.
Im sure the fuel tank is 55 litres... Just cost me £62 to put 52 litres in and I was almost on the 0 line (5 miles left according to trip meter) and managed 365 miles to the previous tank.