This excerpt taken from the PBR 6-K filed May 2, 2005.
4. Valuation Methodology of the Assets
If Petroquisa elects to exercise the Option, Petroquisa must deliver written notice to Odebrecht, Norquisa and ODBPAR on or prior to October 14, 2005 informing them of its decision to commence the valuation process of the Assets in order to allow for the eventual exercise of the Option.
The Option Shares will be valued based on the economic value of Braskem, which will be calculated using the discounted cash flow method, without giving effect to any control premium, and the value of the Assets to be contributed to Braskem will also be calculated using the discounted cash flow method for each company involved, without giving effect to any control premium and using the same criteria and valuation date (as that used for Braskem).