This excerpt taken from the PBR 6-K filed Mar 31, 2009.
4.2 Statement of income, and current and non-current assets and liabilities
Income, recognized on the accrual basis, includes income, charges and monetary or exchange variations at official index or rates, due on current and non-current assets and liabilities, including, where applicable, the effects of adjustments of assets to market value or realization value, as well as the allowance for doubtful accounts recorded at a limit considered sufficient to cover possible losses on the realization of accounts receivable.
Revenue from the sale of products is recognized in the statement of income when the risks and rewards of ownership have been transferred to the buyer. Revenue from services rendered is recognized in the statement of income in proportion to the stage of completion of the service.