Oil prices rose more than 1 percent on Friday as U.S. sanctions against Iran looked set to tighten supply. However, futures were lower for the week as investors worried that global trade disputes could slow economic growth and hurt demand for energy.
U.S. light crude finished the session up 82 cents, or 1.2 percent, at $67.63 a barrel. Benchmark Brent crude oil was up 72 cents, or 1 percent, at $72.79 a barrel by 2:29 p.m. ET.
For the week, U.S. crude dropped more than 1 percent, posting its sixth straight weekly loss for its worst losing streak since August 2015. Brent was down roughly half a percent this week.
"It's not surprising to see a bit of a bounce back here," said Tariq Zahir. But he said prices would remain under pressure as U.S. gasoline demand slows going into the fall and refiners shut for maintenance, pushing more crude into storage.
"I think it now comes down to the point of what we see in demand numbers."
Escalating trade disputes have dimmed the outlook for economic growth and boosted the dollar, making oil more expensive for consumers using other currencies.
Major emerging economies including China, India and Turkey have seen their currencies slump.
Despite these worries, prices got a boost from the introduction of U.S. sanctions against Iran, which from November will include oil exports.
Although the European Union, China and India oppose sanctions, many are expected to bow to U.S. pressure.
Analysts expect Iranian crude exports to fall by between 500,000 and 1.3 million barrels per day, with buyers in Japan, South Korea and India already dialing back orders.
The reduction will depend on whether buyers of Iranian oil receive waivers that would allow some imports.
The International Energy Agency said on Friday the oil market could see more turbulence later this year.
"The recent cooling down of the market, with short-term supply tensions easing, currently lower prices, and lower demand growth might not last," the IEA said in a monthly report.
"As oil sanctions against Iran take effect, perhaps in combination with production problems elsewhere, maintaining global supply might be very challenging."
Investors are keeping a wary eye on the trade dispute between Washington and Beijing.
In the latest round of levies, China said it would impose additional tariffs of 25 percent on $16 billion worth of U.S. imports.
Although crude was removed from the list, replaced by refined products and liquefied petroleum gas, analysts say Chinese imports of U.S. crude will fall significantly.
U.S. energy companies this week added the most oil rigs since May as drillers follow though on plans to spend more on exploration and production in anticipation of higher crude prices in 2018 than recent years.
Drillers added 10 oil rigs in the week to Aug. 10, bringing the total count to 869, the highest level since March 2015, General Electric's Baker Hughes energy services firm said in its closely followed report on Friday.