This excerpt taken from the PBR 6-K filed Mar 18, 2005.
(s) Investments in quoted companies
Investments in quoted companies whose shares are traded on the stock market are as follows:
The market values of these shares do not necessarily reflect the net realizable values at liquidation of a major block of shares.
(*) As the common shares of the subsidiary PETROQUISA traded on the stock market do not have liquidity, the price for preferred shares was used for purposes of determining market values.