Nigeria's rainy day fund from oil revenue plunged to $376,655.09 at the end of June, from $35.37 million the prior month, amid limited crude exports, biting fuel subsidies and a struggling economy.
The government's accountant general released the figures late on Tuesday but did not give a reason for the steep drop.
Nigeria, typically Africa's largest oil exporter, has struggled to benefit from surging crude prices due to pipeline theft and years of underinvestment that have limited oil exports.
Fuel subsidies have also sapped state coffers, and in the first four months of this year, Nigeria's debt servicing costs outpaced public revenue.
Nigeria's debt costs are usually below revenue. The country for decades has relied on oil revenue to fund its budget, and is trying to broaden its tax base, but is hindered by an archaic tax collection system.
President Muhammadu Buhari has also sought funds to equip the military in recent months, which is trying to tame nationwide insecurity, including an Islamist insurgency in the northeast and roving bands of kidnappers in the northwest. (Reporting by Camillus Eboh and Felix Onuah in Abuja, writing by Libby George; editing by Jason Neely)