OPEC is working on an agreement to cut output but needs Russia's approval
OPEC and its allies are working towards an agreement to cut oil production by at least 1.3 million barrels per day, adding that Russia's resistance to significant production cuts is the main obstacle so far.
OPEC meets on Thursday in Vienna and then talks with allies such as Russia on Friday amid a drop in oil prices due to weak global economic performance and concerns over the oversupply of oil as a result of increased US production.
Saudi Arabia, the world's largest producer, has pointed to the need for deep cuts in production from January but is under pressure from US President Donald Trump to help boost the world economy at lower oil prices.
The crisis in the killing of journalist Jamal Khashoggi at the Saudi consulate in Istanbul in October could complicate any OPEC decision. Trump supports Crown Prince Mohammed bin Salman despite calls by many US politicians to impose tough sanctions on Riyadh.
The sources, three from the Organization of the Petroleum Exporting Countries and an exporter from outside, said the meeting was in a difficult situation and Russia's position would be important to reach an agreement.
"Russia is showing a reluctance," one OPEC source said.
Russian sources said that Moscow could contribute about 140 thousand barrels per day in the cut, but OPEC, which is dominated by countries from the Middle East insists that Moscow cut production between 250-300 thousand barrels per day.
Two OPEC sources said the talks focused on a three-to-3.5 percent reduction in production levels recorded in October, with no exceptions for any member.
"Until these standards are met, OPEC may suffer a decline in oil prices for a period if it chooses to postpone the reduction decision for one or two months," one source said.
"OPEC can always meet again in February and decide on a cut then. Who are unable or unwilling to cooperate will be willing to cut back. "
Qatar said on Monday it would withdraw from OPEC to focus on gas, which could undermine Saudi Arabia's efforts to show unity in tackling falling oil prices.