Libya's effort to sharply boost exports was in question again after fighters loyal to the UN-backed unity government were repelled on Sunday in their attempt to retake control of eastern oil ports from rival forces.
Market participants had expected an increase of 3.4-million barrels, according to a Reuters poll.
Brent crude futures settled up 95 cents, or 2 percent, at $46.83 per barrel.
U.S. West Texas Intermediate (WTI) crude futures CLc1 were down 60 cents at $42.70 a barrel, also the lowest in almost six weeks. The session high was $44.15.
Brent and WTI prices were dragged to multi-week lows on Friday amid worries returning supplies from Libya and Nigeria would add to the global supply glut.
Official data released late on Monday confirmed a rise in Saudi Arabian oil exports in July to 7.622 million bpd, up from 7.456 million bpd in June.
Oil has fluctuated since August's rally on speculation the Organization of Petroleum Exporting Countries and Russian Federation will agree on ways to stabilize the market at the meeting.
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Ministers from all 14 member nations of OPEC, as well as the energy minister of Russian Federation plan to have informal discussions about the oil market in Algiers on September 27 on the sidelines of the International Energy Forum.
Oil producers are to meet on the sidelines of an industry conference in Algeria next week for talks on potentially freezing oil production, ahead of OPEC's all-important policy meeting in November.
Japan's customs-cleared crude oil imports rose 0.5 percent in August from the same month a year earlier, the Ministry of Finance said on Wednesday.
The American Petroleum Institute, a trade group, reported a 7.5 million barrel drop in USA crude inventories for the week ended September 16, versus a 3.4 million-barrel drop forecast by oil market analysts polled by Reuters. OPEC Secretary-General Mohammed Barkindo fanned the bullish flames by saying he thought the potential freeze deal could last one year, or perhaps longer.
"We just can not see how OPEC and Russian Federation would be able to reach a freeze accord and even less so a production cut accord", said Bjarne Schieldrop, chief commodities analyst at SEB Markets.
USA gasoline futures RBc1 opened 0.3 percent higher at $1.4659 per US gallon after rising 2 percent on Friday because of outages on Colonial Pipeline's main gasoline line and in a key unit of BP Plc's BP.L refinery in Whiting, Indiana.
