A meeting between OPEC and non-OPEC oil producers on an agreement to freeze output ran into last-minute trouble in Qatar on Sunday due to what looked like a new spike in tensions between Saudi Arabia and Iran, sources told Reuters.
Oil ministers met with the Qatari emir, Sheikh Tamim bin Hamad al-Thani - who was instrumental in promoting output stability in recent months - in an attempt to rescue the deal designed to bolster the flagging price of crude.
According to two sources, Saudi Arabia said it wanted all OPEC members to participate in the talks, despite insisting earlier on excluding its regional arch-rival Iran because Tehran had refused to freeze production.
"The Saudis changed everything early this morning," an OPEC source said. "They want all OPEC members to join first."
Failure to reach a global deal - the first in 15 years between OPEC and non-OPEC nations - would signal the resumption of a battle for market share between key producers and likely halt a recent recovery in prices.
Brent oil has risen to nearly $45 a barrel, up 60 percent from January lows, on optimism that a deal would help ease the supply glut that has seen prices sink from levels as high as $115 hit in mid-2014.
Saudi Arabia has taken a tough stance on Iran, the only major OPEC producer to have refused to participate in the freeze. Tehran says it needs to regain market share after the lifting of international sanctions against it in January.
Deputy Crown Prince Mohammed bin Salman told Bloomberg that the kingdom would restrain its output only if all other major producers, including Iran, agreed to freeze production.