The Organisation of the Petroleum Exporting Countries (Opec) agreed in Algeria on Sept 28 to limit supply with special conditions given to Libya, Nige­ria and Iran, whose output has been hit by wars and sanctions. The details are meant to be finalised when Opec ministers meet in Vienna on Nov 30.

With two weeks to go, differences persist over details and the prospect of a supply glut persisting in 2017 has weighed on oil prices, which are below $47 a barrel. Crude reached a 2016 high near $54 after the September deal.

Two sources familiar with discussions said efforts were under way to narrow gaps and a final agreement would be reached.

“It is difficult at some points but I don’t see any deadlock,” one of the sources said. “What happened in Algeria gave a lot of hope and impetus and I think people are committed to that.”

One issue has been the level of production at which Iran would be expected to freeze its output.

Sources say Iran wants an output cap of 4 million barrels per day, while other members of the Opec want Iran to freeze supply at about 3.7m bpd.

This issue, several Opec sources told Reuters, was a source of tension at an Oct 28 meeting in Vienna of the High Level Committee, a panel looking at how to divide the Algeria agreement into individual supply limits.