This is the latest and largest in a string of allegations against the firm. Nigeria's president, pledging to crack down on corruption, has his eyes set on the firm as he aims to overhaul the nation's oil industry.
Nigeria's independent body for fiscal oversight alleged on Tuesday that the country's state oil firm has withheld 4.9 trillion naira ($25 billion, 22 billion euros) from government coffers from the beginning of 2011 through 2015.
The accusation by the Revenue Mobilization Allocation and Fiscal Commission is the latest in a growing list of claims leveled against the Nigerian National Petroleum Corporation (NNPC).
Since 2014, the secretary-general of the country's central bank, PricewaterhouseCoopers, the Natural Resource Governance Institute, and just last week, Nigeria's state auditor, had raised alarm that the firm was hoarding funds.
The state auditor claimed NNPC kept $16 billion from the state in 2014 alone.
Nigeria's current president, Muhammadu Buhari, was elected in 2015 with the promise to crack down on corruption and overhaul the country's oil industry.
Since entering office, the president has fired several high-level NNPC staff and pushed forward a restructuring plan to break the firm into a number of smaller companies. Parliament is also set to begin debate next week on a bill to revamp regulations for the country's petroleum industry.
Oil revenue makes up about 70 percent of Nigeria's income, with exports accounting for around $77 billion a year.
The NNPC is constitutionally obligated to hand over its entire revenue, minus expenses, to the state. It has denied claims that it has withheld money, saying the allegations did not properly take expenses into account.
jtm/ (Reuters, AFP)