The Senate on Tuesday approved $52 per barrel as oil benchmark price for the N4.3 trillion 2015 budget.
The federal government had made a final proposal of $65 per barrel of crude oil to the lawmakers after two reviews.
The Minister of Finance, Ngozi Okonjo-Iweala, had in December 2014 presented the 2015 budget to the lawmakers based on a speculated oil production figure of 2.2 million barrels per day.
At its closed door session on Tuesday, the Senate said its decision was due to the fact that the current oil price in the international market was between $60 and $62.
President Goodluck Jonathan had forwarded three different Medium Term Expenditure Framework, MTEF, and Fiscal Strategy documents to the National Assembly between September and December last year with crude benchmark proposals of $77, $73 and $65 per barrel.
Other budget proposals include projected oil production of 2.2782 million barrels per day and average exchange rate of N165 to a US dollar. The dollar currently trades at about N199 to a US dollar as the oil-dependent Nigerian economy continues to suffer from the declining global price of crude oil.