The U.S. government plans to shut Iran's oil exports out of the market from November, demanding that all countries stop buying its oil.
USA crude slipped 2 cents to $72.92.
USA crude futures were down 58 cents at $73.56 per barrel by 12:00 p.m. EDT (1600 GMT), still in sight of Tuesday's 3-1/2-year high above $75.
Oil prices edged up on Wednesday, lifted by a report of declining USA fuel inventories amid the ongoing crude supply outage at Syncrude Canada in Alberta, which usually supplies the United States. If anything, they are driving prices higher as the US defends many of their members for very little $'s. This must be a two way street.
Iran has threatened to block oil exports through a key Gulf waterway in retaliation for United States efforts to reduce Iranian oil sales to zero.
The comments this morning follow on from yesterday's news that Saudi Arabia raised oil output by about 500,000 barrels per day in June.
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Trump urged Saudi Arabia to pump more oil..
OPEC together with a group of non-OPEC producers led by Russian Federation started to withhold output in 2017 to prop up prices.
Oil output cuts by the Organization of Petroleum Exporting Countries and allies including Russian Federation since January 2017 have reduced a glut of crude.
Even so, renewed USA sanctions on Iran against its oil exports look set to tighten supply further.
"A key driver of the rise in prices has been the OPEC-Russia deal to cut oil output, compounded by collapsing Venezuelan production and the United States decision to end the Iran deal", National Australia Bank (NAB) said in its July outlook.
Iranian OPEC Governor Hossein Kazempour Ardebili told Reuters that Trump "should have expected" when blocking Iran's access to the global markets that it would end up as "hostage (to) Saudi Arabia and Russia", who he said had little vested interest in bringing down prices.
An Iranian Revolutionary Guards commander, meanwhile, said Wednesday Tehran might block oil shipments through the Strait of Hormuz, a major route for transporting crude in the Arabian Gulf.