Brent crude futures for delivery in January were up $3.83, or 8.3%, at $50.21 a barrel by 1236 GMT, recovering from a drop of nearly 4% on Tuesday and on course for their biggest one-day move in nine months. Brent crude for delivery in February was up $3.76 at $51.08 a barrel.
US West Texas Intermediate (WTI) crude futures were $3.63 higher at $48.86 a barrel, a one-week high.
The Organisation of the Petroleum Exporting Countries started a meeting at 0900 GMT on Wednesday at its Vienna headquarters to discuss terms of a potential deal to cut production in an effort to prop up prices that have fallen by more than half since 2014 due to oversupply.
A source told Reuters that delegates were now discussing a bigger than expected cut in production of 1.4 million barrels per day (bpd).
A preliminary agreement struck in Algiers in September set an output cap at around 32.5-33 million barrels per day compared with the current 33.64 million bpd.
Heading into the meeting, Saudi Arabia's energy minister, Khalid al-Falih, said the market's fundamentals were moving in the right direction, but he believed the group was "getting close to a deal".
"The extent of the (price) move shows no one wants to miss the boat. There must be a general consensus that there will be a cut, whether it's going to be bullish, I don't know, but it's the domino effect," PVM Oil Associates analyst Tamas Varga said.
An Iraqi delegate said on Wednesday that some form of agreement would be reached and Iran's oil minister also said he was optimistic.
Traders said markets were jittery and prices could swing sharply in either direction depending on developments in Vienna.
Oil fell by nearly 4% on Tuesday on reports of disputes between Saudi Arabia, Iran and Iraq over details of the planned production cut.
Iran and Iraq have been resisting pressure from Saudi Arabia to curtail production, making it harder for the group to reach an agreement on output cuts.
Analysts at Goldman Sachs, Barclays, and ANZ said oil prices would quickly fall to the low $40s a barrel if Opec fails to strike a deal to cut output.