Though Iranian oil makes up a relatively small part of the total, industry experts say consumers in Japan may have to pay more for gasoline and other petroleum-related products if imports are suspended.
Brent crude, the global benchmark, was up 0.58% to $78.09 a barrel on London's Intercontinental Exchange.
OPEC oil output has risen this month to a 2018 high as Libyan production recovered and Iraq's southern exports hit a record, a Reuters survey found, although a cut in Iranian shipments due to USA sanctions limited the increase.
With China and India remaining as customers, Iran will not be fully cut off from the global oil markets from November, when U.S. sanctions against the Islamic Republic's petroleum sector are due to start. USA crude CLc1 was 30 cents higher at $70.10.
"We've been saying we will observe a government decision (on Iranian oil imports), but we can't comment further as we don't disclose information on individual trades", a spokeswoman for wholesaler Showa Shell Sekiyu told AFP on Monday.
"Iranian production is already showing signs of decline, falling by 150,000 bpd last month".
Britain's Barclays bank said on Tuesday that oil markets had changed since 2017 when worries about rising supply were more evident.
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Data released by Baker Hughes Friday showed the United States oil rig count rose by 2 to 862 in the week ended August 31.
In all, companies halted 156,907 barrels per day of oil production, according to estimates Tuesday by the U.S. Bureau of Safety and Environmental Enforcement.
"If the market is deprived of around one million barrel per day supply from Iran, it could tighten the supply in the oil market", said Jain.
The overall volume of the crude oil and condensate that is an ultra-light produced from the field of natural gas is estimated for 64M barrels (2.06M barrels/day), in against to the peak of 92.8M barrels (3.09Mbarrels/day).
S. and other major economies including China and the European Union are expected to hurt oil demand if they are not settled soon.
The second-largest production increase came from Iraq and the United Arab Emirates: each raised daily oil output by 80,000 bbl last month. According to a private survey, export orders have dropped down for the fifth straight month.
"Despite this, OANDA's Innes said it was too early to say whether an economic slowdown would put a serious dent on oil prices". He stated that it was not yet clear whether such economic headwinds would be able to topple oil prices.