PRRT is levied at a rate of 40 per cent of a project's taxable...

PRRT is levied at a rate of 40 per cent of a project's taxable profit (that profit being calculated for PRRT purposes). Taxable profit is the project's income after all project and 'other' exploration expenditures, including a compounded amount for carried forward expenditures, have been deducted from all assessable receipts. PRRT payments are deductible for company income tax purposes.

http://www.ret.gov.au/resources/enhancing/taxation/prrt/Pages/PetroleumResourceRentTax%28PRRT%29.aspx