Nigeria's state-owned oil company has failed to pay the government $16bn (£11bn) in a suspected fraud, according to an official audit.
The Nigerian National Petroleum Corporation (NNPC) provided no explanation for the missing funds, the auditor general told MPs.
Oil revenue accounts for two-thirds of the government's funding.
President Muhammadu Buhari has promised to crack down on corruption since coming to office last May.
The NNPC has not commented on the auditor general's findings.
This finding by the auditor general, while shocking, is not a surprise.
Officials from the previous administration allegedly indulged in wholesale corruption where billions of dollars of oil funds simply disappeared.
When the then central bank governor Lamido Sanusi pointed out that billions of dollars were missing from the treasury, he was sacked from his job.
Nigeria's oil reserves should have been blessing for Nigeria to be used to build infrastructure and invest in social services.
Instead, it has been a curse, a lubricant that has produced massive corruption and dysfunctional governments.
President Buhari was elected on a platform of cleaning up the country's notoriously corrupt politics.
But some officials from the previous administration accuse him of using corruption to pursue a political vendetta, foreign media reports.