This excerpt taken from the SU 6-K filed May 1, 2009.
Exchange of Suncor Shares or Petro-Canada Shares Pursuant to the Arrangement
Suncor, Petro-Canada and Amalco intend for the Arrangement to be treated as a reorganization within the meaning of Section 368(a) of the Code (a "Reorganization"). No ruling from the IRS concerning the U.S. federal income tax consequences of the Arrangement has been obtained and none is expected to be requested. Thus, there can be no assurance that the IRS will not challenge the treatment of the Arrangement as a Reorganization or that, if challenged, a U.S. court would not agree with the IRS. If a U.S. Holder participates in the transaction and makes the election to recognize accrued gain or loss for Canadian tax purposes on the disposition of such U.S. Holder's Suncor Shares or Petro-Canada Shares pursuant to the Arrangement, such transaction should be disregarded for U.S. federal income tax purposes and such U.S. Holder should not be treated as recognizing a gain or loss for U.S. federal income tax purposes as a result thereof.