Among persistent glut worries, Saudi Arabian Energy Minister Khalid al-Falih had discussions with his Venezuelan and Kazakh counterparts about the chances of extending supply cuts through March 2018.
OPEC produced 30.004 million barrels daily last month, the source said, versus 30.113 million bpd in July, with Saudi Arabia, the group's leader and biggest producer, reducing output to 10.022 million bpd, from 10.049 million bpd in July.
In a note Monday, however, analysts at Goldman Sachs said the negative impact on oil demand from Irma will be smaller than Harvey, which made landfall on the Texas coast on August 25. U.S. West Texas Intermediate (WTI) crude futures edged down 0.17% to $47.99 a barrel.
Oil prices still gain some degree of support from expectations of firm global demand and the potential for OPEC output cuts to be extended.
Commenting on the impact on oil production of hurricane Harvey, OPEC said "the USA energy industry appears to be rebounding quickly".
Libyan production-which has undercut OPEC's efforts-fell significantly by 112,300 barrels in August, to 890,000 barrels a day, a result of pipeline closures and disruptions at its oil fields, the report showed. More recently Hurricane Irma left more than seven million homes without electricity in Florida.
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Hurricane Harvey disrupted refinery production in Texas last month-one reason USA crude futures have been lower than the global benchmark. In the first half of this year, crude oil price declined by around 15 percent, which is its worst H1 showing in 19 years.
Crude inventories rose by 6.2 million barrels in the week to September 8 to 468.8 million, compared with analysts' expectations for an increase of 3.2 million barrels.
"The oil market reacted to the Saudi talks", said Tomomichi Akuta, senior economist at Mitsubishi UFJ Research and Consulting told Reuters.
Official data from the Energy Information Administration will be released Wednesday.
"We're waiting for our refineries to all get going", he said, "On the east coast we don't have enough gasoline so we have to import more product from Europe, which adds a boost to Brent".