The impact on Iran's oil exports will depend on how buyers in Asia and Europe react to USA sanctions, which may not be clear for months.
Additionally they view USA drilling constrained by pressure organizations to work out capital area from the face of rising costs.
A loss of 500,000 bpd of Iranian crude oil supply would push up oil prices by around $6.20 a barrel, according to Goldman Sachs.
U.S. West Texas Intermediate (WTI) crude futures were down 15 cents, or 0.2 percent, at $71.21 a barrel after hitting a November 2014 high of $71.89 per barrel on Thursday. Resulting rising oil prices would have a mixed impact across the region, driving prices higher for some countries that rely heavily on imports, such as Japan, while boosting revenues for exporters such as Indonesia. "There's not a lot of room for error". Furthermore, it concluded a bilateral trade deal with Iran in 2016 meant to boost Japanese investment in the country.
Another European buyer, Italy's Eni ENI.MI , said it is buying 2 million barrels a month of Iranian crude as part of a contract running to year-end, adding any new sanctions would take six months to kick in. During the last round of sanctions, Iran's oil supplies fell by around 1 million barrels per day (bpd), but the country re-emerged as a major oil exporter after sanctions were lifted in January 2016. Sales to Europe are seen by analysts as the more likely to be reduced by the sanctions.
Analysts had little hope that opposition to the U.S. action would prevent sanctions from going ahead.
But major nuclear proliferation experts around the world, as well as many of America's own top military generals and European governments, have unilaterally supported the Iran deal, arguing that it is the best way to keep Iran from pursuing nuclear enrichment.
The energy sector in equity markets rallied, helping lift European stocks, a gauge of world equity performance and the broad USA market. They will grumble and accept it.
"Waivers seem a sensible course of action", the third source said, referring to potential exemptions from the latest US sanctions.
"We believe the previous 1 million-bpd limit for exports (imposed during previous sanctions) will be reimposed".
Major oil producers from Opec and non-Opec members including Russian Federation, the world's top producer, are linked to a deal until the end of the year to cut output by 1.8 million bpd to support prices.
Trying to ease market concerns, Saudi Arabia on Wednesday said it would work with other producers to lessen the impact of any shortage in oil supplies.
Meanwhile, Saudi Arabia - which has long called for sanctions to be re-imposed on Iran - has pledged to "mitigate" the effects of the sanctions. That sanctions will return, cutting a portion of Iranian exports off global markets is only one facet. US heating oil futures surged to $2.2258 a gallon, the highest since February 2015.
The 10-year U.S. Treasuries yield ticked up more than two basis points to 2.991 per cent. The agency has raised its forecasts every month since last August.
Saudi Arabia hoped that the global community would take a united and decisive stance on Iran and its hostile destabilizing actions in the region, including its support to the Syrian regime of Bashar Assad that has committed the most atrocious crimes against its people.