81 AGL Energy Limited Annual Report 2011 2011 2010 $m $m Deferred tax balances Deferred tax assets/(liabilities) arise from the following: Unbilled revenue  (208.4) (198.6) Allowance for doubtful debts  19.4 19.1 Other receivables  (9.8) (10.0) Exploration and evaluation assets  (154.2) (148.2) Oil and gas assets  (34.2) (5.8) Property, plant and equipment  (109.2) (87.2) Defined benefit superannuation plans  12.2 16.0 Payables and accruals  40.7 39.5 Provisions  71.0 66.8 Derivative financial instruments  57.0 143.2 Unearned revenue  6.5 0.5 Share issue transaction costs  – 1.3 Other  6.3 (2.2) Net deferred tax liability  (302.7) (165.6) Net deferred tax liability is split as follows: Deferred tax assets recognised in the statement of financial position  – – Deferred tax liabilities recognised in the statement of financial position  (302.7) (165.6) (302.7) (165.6) Unrecognised deferred tax assets Deductible temporary differences  55.0 69.7 Tax consolidation The Parent Entity and its wholly-owned Australian resident subsidiaries formed a tax-consolidated group under Australian taxation law with  effect from 25 October 2006 and are therefore taxed as a single entity from that date. AGL Energy Limited is the head entity in the  tax-consolidated group. The members of the tax-consolidated group have entered into a tax sharing and tax funding agreement. The tax funding agreement  requires payments to/from the head entity equal to the current tax liability (asset) assumed by the head entity and any tax-loss deferred  tax asset assumed by the head entity. The payments are recorded as intercompany receivables/payables. As a result of retrospective changes to the tax consolidation legislation enacted in June 2010, AGL has recognised a further tax benefit of  $5.5 million (2010: $85.5 million) relating to tax deductions which are available for the tax value allocated to certain derivative assets in  place at the time of the merger/demerger transaction with Alinta Limited in October 2006. AGL received tax refunds of $72.4 million  during the 2011 financial year and expects to receive further tax refunds of $22.1 million. These amendments also resulted in a change to  deferred tax liabilities of $3.5 million.