Brent crude oil pared gains but remained above $113 a barrel on easing concerns that an insurgency in Iraq would trigger a sudden and significant halt in its oil exports.
"The market in general is trying to assess the risks on Iraq. There was a big market reaction and then the IEA (International Energy Agency) said it did not see a risk to supplies so the volatility is reflecting this," Olivier Jakob at Petromatrix consultancy said.
Most of Iraq's current oil exports come from south of Baghdad, still far from the Islamist rebel fighters. Should they reach south of Baghdad, analysts expect them to encounter much greater resistance.
Iraqi exports from the north are considered safe for the moment, analysts said, as the major Kirkuk oil hub is held by Kurdish forces.
“While the Iraqi military faces low morale issues in the north, Shia fighters would prove much more resilient in protecting their homes and provinces in southern Iraq, and Sunni insurgents have no local support,” Ayham Kamel, director of the Middle East and North Africa at Eurasia Group, wrote in a research note earlier this week.
Brent was up 55 cents at $113.57 per barrel as of 1142 GMT, off a peak of $114.69, its highest since September. It gained more than $3 on Thursday. U.S. crude was up 48 cents at $107.01, off a high of $107.68, also a nine-month high. A day earlier it gained $2.13. Brent was set to gain more than 5 percent this week, the biggest weekly rise since last July, while U.S. crude was on track for its biggest jump since December.
"You want to have a premium as Iraq is more unstable than last week, but with no disruptions, how much can you keep," Jakob at Petromatrix said.
The United States has threatened military action against Islamist militants who have taken towns and cities in Iraq, raising concerns over its oil exports.
The militants, a Sunni offshoot of al Qaeda, were moving into two towns in the eastern province of Diyala after security forces abandoned their posts.
The IEA played down fears over the possible sudden loss of oil exports from Iraq in its monthly Oil Market Report.
"Concerning as the latest events in Iraq may be, they might not for now, if the conflict does not spread further, put additional Iraqi oil supplies immediately at risk," the Paris-based agency said.
Analysts say oil markets are finely balanced at the moment and another significant blow to supply could push up prices even further.
The IEA said on Friday that OPEC would need to produce one million barrels per day (bpd) more oil on average in the second half of 2014 to balance the global market, which will see a steep seasonal spike in demand.
The agency raised its estimate for demand for OPEC crude oil in the second half of this year by 150,000 bpd from its forecast last month to an average of 30.9 million bpd.
The bullish assessment contrasted with the view of OPEC, which on Thursday said extra production would be more than sufficient to meet growing demand.
The cartel of 12 exporters said global oil inventories were comfortable. U.S. stockpiles were high and commercial stocks in the large developed economies were sufficient at the end of April to meet almost two months of consumption.
Overshadowed was U.S. data which showed retail sales rose less than expected in May and first-time applications for jobless benefits increased last week.
China's industrial output rose 8.8 percent in May from a year earlier, while retail sales rose 12.5 percent, the National Bureau of Statistics said, matching forecasts and helping assure markets of a stable Chinese demand outlook.
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