In the previous round of sanctions against Tehran, in which the European Union had taken part, Iranian oil exports plummeted by more than half to below 1 million barrels per day.
PDVSA has notified customers in recent days that they must agree to load crude in Venezuela's open waters rather than its ports to avoid a possible declaration of force majeure that would temporarily interrupt some of its supply contracts.
Meanwhile, Venezuelan oil exports have been crippled as the Latin American nation spirals toward economic collapse.
The cause of Friday's losses is ironic considering so much focus has been paid over the past few weeks to the widespread argument that the crude market is tightening rapidly (due to dramatic declines in output from troubled major producers such as Venezuela), and to the point where even the mighty US shale industry won't be able to meet demand.
But many European companies are already severing ties with Tehran for fear of facing secondary sanctions from the United States, which could mean losing access to the U.S. dollar clearing system.
Next week's discussion between Russian Energy Minister Alexander Novak and his Saudi counterpart Khalid Al Falih in Moscow may be a prelude to a broader gathering of Opec members and allied producers later this month.
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The US has appealed to OPEC to raise output amid a run-up in domestic gasoline prices, even as US crude output surges. "In the end, OPEC will make sure to tread carefully". U.S. West Texas Intermediate (WTI) crude futures ended 21 cents lower at $65.74 a barrel.
Against that backdrop, Russian President Vladimir Putin is scheduled to meet Saudi Crown Prince Mohammed bin Salman at a World Cup soccer match on June 14.
"They're all seeming to push back on the Saudis' push to raise production", said John Kilduff, a partner at Again Capital Management in NY.
Money managers cut bullish ICE Brent crude oil bets by 13,810 net-long positions to 438,186, weekly ICE Futures Europe data on futures and options showed. "The US tried it last time against Iran, but oil prices got to $140 a barrel", he said.
In other commodities, wholesale gasoline stayed at US$2.12 per gallon, while heating oil shed 0.7 percent to US$2.16 per gallon and natural gas fell 1.4 percent to US$2.89 per 1,000 cubic feet.
Despite Friday's decline, Brent remains more than 15 percent above its level at the start of the year.