This excerpt taken from the PBR 20-F filed Jun 30, 2005.
DOMESTIC SALES OF NATURAL GAS TO LOCAL DISTRIBUTION COMPANIES
Commitments and Sales Contracts
Gas purchase commitments. Under our contracts with YPFB for the purchase of natural gas, we have agreed to purchase minimum volumes of natural gas from Bolivia at a formula price that varies with the price of fuel oil. We have purchased and paid in 2004, 2003 and 2002, approximately U.S.$638 million, U.S.$452 million and U.S.$260 million, respectively. During 2003 and 2002 we purchased less than the minimum volumes set under our agreement with YPFB, and therefore we were obligated to make payments of U.S.$29 million and US$52 million, respectively. Set forth below are the minimum volumes we have agreed to under these contracts, together with an estimate of the amounts we are obligated to pay for such minimum volumes: