Well, my 100 airplane airline has a WEEKLY fuel bill of around 10 000 000$, so 5% of that are 500 000$; the MONTHLY fuel contract fee is 350 000$, around 80 000$ a week.
So the fuel contract saves my airline around 400 000$ a week.
Don't mix up weekly and monthly based numbers here

Of course it's a factor of airline size. A 10 airplane airline isn't going to benefit, the bigger you get the more such a contract saves you.
Hope this clears things up,
greets,
Cedric