Non-OPEC oil production giant Russia confirmed on Tuesday that it would not attend the OPEC gathering, but added that a meeting between the group and non-affiliated producers at a later stage was possible, as reported by Reuters.
Brent crude futures LCOc1 were trading at $47.69 per barrel at 07:41 GMT, down 55 cents, or 1.14 percent, from their last close.
U.S. West Texas Intermediate crude futures CLc1 were down 51 cents, or 1.06 percent, at $46.58 a barrel.
Read alsoReuters: Oil prices fall over doubts of planned crude output cutThe Organization of the Petroleum Exporting Countries (OPEC) is meeting officially in Vienna on Wednesday to discuss a planned production cut in an effort to curb overproduction that has dogged markets and more than halved prices since 2014.
"Volatility is set to be high in the oil market in the days ahead," Barclays bank said on Tuesday.
"I still think they need to do a deal even though my confidence has dropped back to coin toss levels," said Greg McKenna, chief market strategist at Australian brokerage AxiTrader.
Intense negotiations would be needed on Wednesday to cement a deal, Goldman Sachs (GS.N) said.
"The latest headlines suggest that while there is a broad agreement on the rationale for a cut, political considerations and country level quota negotiations are so far preventing a deal from being reached," the bank said.
There remains disagreement among OPEC members over which producers should cut by how much.
If OPEC agreed a production cut to 32.5 million barrels per day (bpd), down from 33.82 million bpd in October, crude prices would likely rise to the low $50s per barrel, Goldman said.
Both Goldman and Barclays said that oil prices would quickly move above $50 per barrel if a production cut is agreed by OPEC.
"If no deal is reached, our expectation of rising (crude) inventories through 1H2017 would warrant prices averaging $45 per barrel through next summer," Goldman said.
However, the "price risk is likely skewed to the upside heading into Wednesday," it added, saying a move to below $40 per barrel would be difficult to sustain.
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.