Haftar's blockade on oil facilities cost Libya $1 billion
Groups allied to militia commander Khalifa Haftar launched their blockade of eastern Libya's main oil terminals on 18 January, AFP reported on Wednesday.
Production has since declined from "more than 1.2 million to 187,000 barrels a day", a fall of more than 80 percent, according to an update on the NOC website posted on Wednesday.
The blockade started the day before an international summit in Berlin started, which called for an end to foreign interference in Libya's conflict and a resumption of peace efforts.
The ensuing cuts in production due to storage capacity problems has caused "losses estimated at $931 million", the NOC said.
Exports were suspended at the ports of Brega, Ras Lanouf, Al-Sidra, Al-Hariga and Zweitina in the country's "oil crescent", the conduit for the majority of Libya's crude exports.
The NOC had previously condemned the closure of valves at a pumping station in the southwest of the country that ceased production at the major Al-Sharara and Al-Fil oil fields.
The blockade of the country's main source of revenues was a protest against Turkey's despatch of troops to shore up support for Haftar's rivals.
Turkey has backed the Tripoli-based Government of National Accord, while Haftar has support from Russia, the UAE and Egypt.
Libya has been mired in chaos since a 2011 overthrow of longtime dictator Muammar Gaddafi, with rival administrations and militias vying for power.
The conflict deepened last April when Haftar, whose forces control much of Libya's south and east, launched an assault to seize Tripoli.
The embassies of the US and the UK, as well as the EU delegation in Libya, called for a resumption of NOC operations, warning of the risks of exacerbating the humanitarian hardships facing the country.