Opec tentatively agreed an oil output cut on Thursday but was waiting for a commitment from non-Opec heavyweight Russia before deciding the exact volumes for a production reduction aimed at propping up crude prices, two sources from the group said.
Russian Energy Minister Alexander Novak flew home from Vienna earlier for talks with President Vladimir Putin in St Petersburg.
Novak returns to the Austrian capital today for discussions among Opec and the group's allies.
The price of crude has fallen almost a third since October but US President Donald Trump has demanded the Organisation of the Petroleum Exporting Countries make oil even cheaper by refraining from output cuts.
"We hope to conclude something by the end of the day tomorrow (Friday)...We have to get the non-Opec countries on board," Saudi Energy Minister Khalid al-Falih told reporters before the Opec meeting started. "If everybody is not willing to join and contribute equally, we will wait until they are."
Al-Falih said all options were on the table.
Possible output cuts by Opec and its allies ranged from 0.5mn-1.5mn bpd, and 1mn bpd was acceptable, he said.
Opec's closed-door meeting concluded after 4-1/2 hours without yielding concrete figures, several delegates said, adding that many countries including Iran, Libya and Venezuela were seeking exemptions from cuts.
"1mn bpd may disappoint many. But should the cut be from a September or October baseline, rather than November, the net impact would be sufficient to limit storage builds," Greg Sharenow, executive vice-president for Pimco, said on the sidelines of the Opec meeting.
"It is unlikely to spark a meaningful price rally, but also will not be so dire either. In many respects it is the middle road, which may be the optimal solution," said Sharenow, who helps manage a $15bn commodities fund at the $1.77tn US investment management firm.
Opec delegates have said the group and its allies could cut by 1mn bpd if Russia contributed 150,000 bpd of that reduction.
If Russia contributed around 250,000 bpd, the overall cut could exceed 1.3mn bpd.
Novak said yesterday that Russia would find it harder to cut oil output in winter than other producers because of the cold weather.
Oil prices have crashed as Saudi Arabia, Russia and the UAE raised output since June after Trump called for higher production to offset lower exports from Iran, Opec's third-largest producer.
Russia, Saudi Arabia and the US have been vying for the position of top crude producer in recent years.
The US is not part of any output-limiting initiative due to its anti-trust legislation and fragmented oil industry.
Iranian exports have plummeted after the US imposed fresh sanctions on Tehran in November.
But Washington gave sanctions waivers to some buyers of Iranian crude, further raising fears of an oil glut next year.
"Hopefully Opec will be keeping oil flows as is, not restricted. The world does not want to see, or need, higher oil prices!" Trump wrote in a tweet on Wednesday.
Iranian Oil Minister Bijan Zanganeh said yesterday he would support a cut as long as Iran did not need to reduce its own output.
