Also if you want to save money adjusting driving style makes a huge difference. When I first got my car I was rough, I was over reving, leaving it late to change gears, speeding to 30mph only to have to then suddenly stop.
I am now anticapting these more so slowly down earlier, changing gear a lot quicker and driving a lot smoother. I put £10 of fuel in when it was 96p, my tank was so empty it was below red, have done 77 all city miles and the needle is slightly above red. When driving rough it was empty by 60.