Under the previous round of sanctions on Iran, OPEC's third-largest producer had used this strategy-keeping oil in floating storage off its coasts-when the US and European sanctions in 2012-2016 cut its ability to export oil.
Benchmark Brent crude futures rose 47 cents to $79.53 a barrel, by 1649 (GMT).
"Things are tightening up", the agency said in its monthly report, but added: "As we move into 2019, a possible risk to our forecast lies in some key emerging economies, partly due to currency depreciations versus the USA dollar raising the cost of imported energy".
Brent crude futures climbed 38 cents, or 0.5 percent, to $77.75 a barrel.
Traders said this pulled wide open the discount of U.S. WTI crude versus Brent to around $10 per barrel, the biggest since June.
"Crude oil production in OPEC rose month-on-month by 278,000 barrels a day in August, to 32.57 million bpd in August", the oil cartel said.
"The path of least resistance for oil prices, given the supply fundamentals, remains up", Harry Tchilinguirian, oil strategist at BNP Paribas, told Reuters Global Oil Forum.
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Opec, the Organization of the Petroleum Exporting Countries that accounts for 40% of global production, cut its forecast for oil demand growth next year in its monthly report.
US Energy Secretary Rick Perry met with Saudi Energy Minister Khalid al-Falih on Monday in Washington, the US Energy Department said, as the Trump administration encourages big oil-producing countries to keep output high ahead of the renewed sanctions.
Russian energy minister Alexander Novak said global oil markets were fragile due to geopolitical risks and supply disruptions.
Russia, the United States and Saudi Arabia are the world's three biggest oil producers by far, meeting around a third of the world's nearly 100 million barrels per day (bpd) of daily crude consumption.
Combined output by these three producers has risen by 3.8 million bpd since September 2014, more than the peak 3 million bpd Iran has managed during the last three years.
Earlier today, according to the Russian news agency, TASS, Russia's Energy Minister Alexander Novak said that the OPEC and its allies could sign a new long-term cooperation deal when they meet in early December and added that output quotes could remain in place after 2018.
U.S. crude stocks fell 5.3 million barrels in the week to September 7 to 396.2 million barrels, the lowest since February 2015 and about 3 percent below the five-year average for this time of year, the U.S. Energy Information Administration (EIA) said on Wednesday.