Libya's Tripoli-based National Oil Corporation (NOC) said on Wednesday that four export terminals were being reopened after eastern factions handed over the ports.
Force majeure, a legal waiver on contractual obligations, was lifted on the ports of Ras Lanuf, Es Sider, Zueitina and Hariga, it said in a statement.
"Production and export operations will return to normal levels within the next few hours," it said.
The ports were closed last month amid a struggle for control by rival factions, slashing Libya's national production by as much as 850,000 barrels per day (bpd).
Ras Lanuf and Es Sider were shut when armed opponents of eastern-based commander Khalifa Haftar attacked them on June 14.
The attack was repelled a week later, but eastern officials aligned with Haftar blocked operations at both terminals as well as at Zueitina and Hariga, saying they would take control of exports through a rival NOC based in the east.
On Wednesday the NOC commended Haftar's Libyan National Army (LNA) for "putting the national interest first" by handing back the ports.
Eastern oil facilities guards and the head of the rival NOC, Faraj Said, confirmed the ports were reopening, although Said told Reuters that Ras Lanuf and Es Sider, which have been damaged in repeated rounds of fighting, required maintenance work.
"The ports of Zueitina and Hariga are now open for any tankers carrying a contract. Ras Lanuf and Es Sider need some maintenance," he said.