SAO PAULO — Brazil’s pre-salt oil reserves for the first time account for more than half of the country’s production of oil equivalent, the National Petroleum Agency said Wednesday.

The agency said on its website that Brazil extracted 1.685 million barrels of oil from pre-salt reserves in December, which was 50.7 percent of the overall production of 3.325 million barrels.

The reserves lie offshore in the Atlantic more than a mile (1.6 kilometers) below the ocean’s surface and under an additional 2.5 miles (4 kilometers) of soil and corrosive salt.

According to the agency, Brazil’s pre-salt reserves accounted for 40 percent of total production in 2016.

In October, Brazil auctioned the rights to develop deep water oil fields, the first time that private and foreign companies were given the chance to operate pre-salt reserves themselves. Previously, state-run Petrobras needed to have at least a 30 percent stake in any oil operation, but President Michel Temer is pushing to increase privatization and attract more international investment.

On Wednesday. Temer signed the concession agreements from the October auctions that netted Brazil 6.15 billion reals, or about $1.8 billion.