Brent crude prices rose in choppy trading on Thursday, supported by supply concerns and geopolitical tensions while U.S. crude fell as oil companies assessed damage after Hurricane Isaac's trek through the region.
A possible strike by Norway's oil services workers, upcoming North Sea maintenance and the ongoing dispute over Iran's nuclear program continue to support Brent prices.
Brent remained on pace to post a second straight monthly gain of more than 7 percent, with U.S. crude also on track for a 7 percent rise in August.
"Brent has more geopolitical risk associated with it and it is North Sea maintenance season," said Gene McGillian, analyst at Tradition Energy in Stamford, Connecticut.
Phillips 66 said a Louisiana refinery was at least partially flooded, but no major damage to offshore oil production platforms has so far been reported as companies operating in the U.S. Gulf Coast region assess the impact of Isaac, now downgraded to a tropical storm.
Anadarko said it expects to start restaffing shut Gulf of Mexico platforms on Friday and that remote monitoring shows all five of its shut platforms were intact.
Iran is preparing for a possible major expansion of uranium enrichment in a fortified underground facility, the U.N.'s International Atomic Energy Agency said in a report on Friday.
The IAEA said "no concrete results" have been reached in talks with Iran this year and that important differences remain. underlining Tehran's defiance in the face of Western pressure and the threat of an Israeli attack.
Brent October crude edged up 16 cents to $112.70 a barrel by 1:50 p.m. EDT (1750 GMT), having swung from $112.25 to $113.44.
U.S. October crude was down $1.10 at $94.39 a barrel, having fallen to $93.95 during the session and needing to finish the week above $96.15 to avoid breaking a string of four straight weekly gains.
Ahead of front-month September contract expirations, U.S. RBOB gasoline futures edged lower, while heating oil rose about a penny.
Gasoline is on pace for a 5 percent monthly gain, with heating oil on track for a 10 percent rise in August.
Investors await a Friday speech by U.S. Federal Reserve Chairman Ben Bernanke at a gathering of central bankers and economists in Jackson Hole, Wyoming, looking for any hint of a third round of quantitative easing, with more stimulus expected to weigh on the U.S. dollar and boost dollar-denominated oil.
OPEC OUTPUT SEEN UP IN AUGUST
Supply from the 12-member Organization of the Petroleum Exporting Countries rose in August to 31.53 million barrels per day, up from 31.30 million bpd in July, according to a Reuters survey.
Iran's oil shipments have risen slightly in August and indicated Saudi Arabia and its Gulf Allies have not been pumping more this month, the survey showed.
A European Union embargo on importing Iranian oil is completing its second month. (Additional reporting by Julia Payne in London and Florence Tan in Singapore; Editing by Bob Burgdorfer and Marguerita Choy)