This excerpt taken from the PBR 20-F filed Jun 30, 2005.
Crude oil prices
International oil prices increased at a record rate in 2004. The main factors driving this price increase include:
Although our oil prices are influenced by international oil prices, the price we charge for oil is generally lower than international prices. The main reasons for such spread relate to the fact that the oil we produce is heavier, which requires more refining expenses, and there is less refining capacity available capable of processing our heavy oil. This spread increased in 2004.