This excerpt taken from the PBR 20-F filed May 22, 2009.
Backup Withholding and Information Reporting
A U.S. holder may, under certain circumstances, be subject to backup withholding with respect to certain payments to that U.S. holder, unless the holder (i) is a corporation or comes within certain other exempt categories, and demonstrates this fact when so required, or (ii) provides a correct taxpayer identification number, certifies that it is not subject to backup withholding and otherwise complies with applicable requirements of the backup withholding rules. Any amount withheld under these rules generally will be creditable against the U.S. holders U.S. federal income tax liability. While non-U.S. holders generally are except from backup withholding, a non-U.S. holder may, in certain circumstances, be required to comply with certain information and identification procedures in order to prove entitlement to this exemption.