No easy answer to your question unfortunately Varig.
Jet A-1 (I'm assuming this is the fuel you're referring to) is generally priced at a surplus or discount* to a continuously updated market price marker known as Platts. Platts prices are only availabe to subscribers, and subscription is fairly expensive.
*The size of the surplus or discount is negotiated between the airline/fuel supplier.
To give you a guide, here are some recent northwest Europe prices (US dollars/metric ton)
23-26 Jan 633.25
16-20 Jan 619.00
9-13 Jan 588.10
4th Quarter 05 592.00
3rd Quarter 05 631.26
2nd Quarter 05 555.87
1st Quarter 05 485.41
As you can see, the price can swing quite considerably. However airlines can guard against this (to some extent) by a financial process known as "hedging".
Hope the above helps in your research
