The Customs department failed to realise revenue of Rs 20,808 crore demanded up to March 2015, due to delay in assessment, official auditor CAG has said. "Customs revenue of Rs 20,808 crore demanded up to March 2015 was not realised by the department at the end of FY15. Of this, Rs 6,211 crore was undisputed. Eight zones accounted for 76 per cent of total revenue arrears pending during FY15," said the CAG Compliance Audit Report on 'Indirect Taxes-Customs' tabled in Parliament on Friday. The report said there were abnormal delays in finalisation of provisional assessment and consequent postponement in realisation of revenue. "More than 36,000 cases with bond value exceeding Rs 1,08,389 crore were pending beyond six months for collection of customs revenue," it said.