Oil prices fell as much as 4 percent on Tuesday on signs leading oil exporters in OPEC were struggling to agree on a deal to cut production to reduce global oversupply.
The Organization of the Petroleum Exporting Countries will meet in Vienna on Wednesday aiming to implement a deal outlined in September to cut output by around 1 million barrels per day (bpd), from around 33.82 million bpd in October.
But Iran and Iraq were resisting pressure from Saudi Arabia to curtail oil production, making it hard for OPEC to reach an agreement. That has led some analysts to suggest the meeting may fail to reach a deal or produce one that is unworkable.
"The inability to arrive at a framework for a reasonable agreement after 2½ months of Saudi driven discussions strongly suggests any formal communique to restrain output will be a watered down version," Jim Ritterbusch, president of Chicago-based energy advisory firm Ritterbusch & Associates, said in a note.
Ritterbusch, however, said he believes OPEC had a better than 50 percent chance of reaching an agreement, which should offer some near-term price relief. He noted the burden of actual curtailments would likely fall on the Persian Gulf producers, especially the Saudis.
Documents prepared for a ministerial OPEC meeting on Wednesday propose the group cut production by 1.2 million bpd from October levels, an OPEC source familiar with the papers said.
The papers for the meeting also propose Saudi Arabia reduce production to 10.07 million bpd from 10.54 million bpd in October and that Iran freeze output at 3.797 million bpd, according to the source.
Iran's oil minister earlier on Tuesday said the country was prepared to leave its oil production at levels to which OPEC had agreed at its September meeting in Algeria.
OPEC, which accounts for a third of global oil production, agreed in September to cap output at around 32.5-33.0 million barrels per day versus the current 33.64 million bpd to prop up oil prices, which have halved since mid-2014.
OPEC said it would exempt Iran, Libya and Nigeria from cuts as their output has been crimped by unrest and sanctions.
Non-OPEC producer Russia confirmed on Tuesday it would not attend the OPEC gathering, but added that a later meeting was possible.
Indonesian Energy Minister Ignasius Jonan said he was not sure OPEC would clinch a deal to limit oil output when it met.
"I don't know. Let's see. The feeling today is mixed," he told reporters when asked about the prospects of a deal.
Intense negotiations would be needed on Wednesday to cement a deal, Goldman Sachs analysts said. If OPEC agreed to cut production to 32.5 million bpd, crude prices would likely rise to the low $50s a barrel, Goldman said.
"If no deal is reached, our expectation of rising (crude) inventories through the first half of 2017 would warrant prices averaging $45 per barrel through next summer," Goldman said.
In Asia, OPEC's biggest customer region, oil importers made clear that they would not be happy with an artificial supply cut that hikes prices, and that in case of a cut they would seek more supplies from outside OPEC.
In the United States, analysts polled by Reuters ahead of weekly inventory reports from the American Petroleum Institute (API) industry group later on Tuesday and the U.S. Energy Information Administration (EIA) on Wednesday estimated, on average, that crude stocks increased about 900,000 barrels in the week to Nov. 25..