Nigeria's state oil company withheld 3.2 trillion naira ($16 billion) in revenues from the federal government in 2014, the auditor-general said on Monday, the same year that the then central bank governor was suspended after making similar claims, Reuters reports.
Constitutionally, the Nigerian National Petroleum Corporation (NNPC) must hand over its oil revenue - which makes up about 70 percent of total income - and money is then paid back based on a budget approved by parliament.
President Muhammadu Buhari won office last May in Africa's biggest oil-producing nation, promising to end the graft and mismanagement that has stunted the continent's biggest economy.
Nigeria is going through its worst economic crisis for years due to tumbling crude prices. Buhari has said mind-boggling amounts of oil money were stolen, leaving state coffers virtually empty when he came to power and deepening the crisis.
The report by Auditor-General Samuel Ukura stated that the findings were based on an "examination of NNPC mandates to CBN (Central Bank of Nigeria) on Domestic Crude Oil Sales and Reconciliation Statement of Technical Sub-committee of Federation Account Allocation Committee (FAAC) meeting held in January 2014".
"Amount not remitted to FAAC was N3,234,577,666,791.35," the auditor-general said in his report.
A spokesman at NNPC said he was unable to comment. According to the latest figures on OPEC's website, Nigeria's oil exports are worth about $77 billion a year.
In 2014, the central bank governor, Lamido Sanusi, was suspended after accusing the NNPC of failing to pay $20 billion into government accounts between January 2012 and July 2013.
Although the constitution requires NNPC to hand over its oil revenue, the act establishing the state oil company allows it to cover costs before remitting funds to the government.
Buhari, who sacked senior NNPC managers just weeks after his inauguration, has approved splitting the company into upstream, downstream, gas power marketing, refinery groups, and ventures divisions in an attempt to improve transparency.
Ukura, who presented his findings in a report to lawmakers at the national assembly, said other government ministries and agencies had also failed to remit funds, taking the total money withheld to 3.3 trillion naira for 2014.
Gas export sales worth $346 million were stated to have been paid to the government but "no statements or documents were made available to confirm the receipts", his report said.