The State Department has ordered buyers to cut oil imports from Iran by November 4.
Against a backdrop of falling output from other key OPEC countries, analysts say barrels could hit $100.
Less than a month before another round of US sanctions against Iran take effect, analysts say hundred-dollar oil could be on the horizon.
The Trump administration has called on buyers to cut off oil imports from Iran in efforts to pressure the third-largest OPEC producer to change its behavior, a move that could squeeze global supply and pressure prices that are already at four-year highs. Brent, the international benchmark, is currently trading at around $85 a barrel.
"Higher oil prices seem inevitable and, in our view, $100 per barrel is easily within reach," economists from the Bank of America Merrill Lynch wrote in a recent research note, citing a looming dropoff in Iranian production.
Iran's crude exports have fallen more than expected ahead of the sanctions, even as the Islamic Republic offers Asian customers the cheapest prices in more than a decade versus Saudi grade. According to tanker data compiled by Bloomberg, shipments dropped by just over a quarter million barrels per day in September to the lowest level since 2016.
In hopes of preventing Tehran from moving forward with its nuclear program, European officials have been working to protect Iranian oil sales from US sanctions. But the Trump administration has portrayed those efforts as implausible, threatening to penalize companies that try to circumvent its policy.
"The European Union is strong on rhetoric and weak on follow-through," John Bolton, the national security adviser, said in a conference speech last month. "We do not intend to allow our sanctions to be evaded by Europe or anybody else."
President Donald Trump has looked to other oil producers to pick up the slack ahead of midterm elections, but output disruptions in key OPEC countries present limits. Helima Croft, a former CIA analyst who is now head of commodities research at RBC, said plummeting production in Venezuela and Angola leaves little room to balance other supply risks in Libya, Nigeria and Iraq.
"The countries that can increase are very small in number," she said, adding that there are questions about how long Russia can keep raising output. "It's really only Saudi Arabia at this point."
Following requests from the White House, Riyadh said earlier this year it could increase output by a "measurable amount." While Saudi Arabia accounts for the lion's share of OPEC production, some analysts are skeptical it has enough spare capacity to fill the gap while maintaining adequate reserves.
Trump has repeatedly taken aim at OPEC for rising energy prices, even after it came to a rare agreement to ease production restrictions in June. The 15-member group has been coordinating output levels since 2016 in efforts to tackle a global oil glut.
"We protect the countries of the Middle East, they would not be safe for very long without us, and yet they continue to push for higher and higher oil prices!" the president said in a recent tweet. "We will remember. The OPEC monopoly must get prices down now!"
That strategy may have encouraged member countries to increase production in the past, Croft said, but will likely become less effective as the global oil cushion shrinks. Output from the 12 countries bound by the supply-cutting agreement actually fell by 70,000 barrels per day in September, a Reuters survey found.
"With Trump and these tweets, I think there are diminishing returns," she said. "In terms of going forward, we're looking at an ever-shrinking pool of OPEC barrels. You can yell at them. But if they don't have the barrels, they don't have the barrels."
While the administration has said it may grant sanction waivers to avoid supply shocks, a tactic used in the Obama era, it has still maintained an objective of sending Iranian oil exports to zero. The White House did not respond to an email requesting comment.
At $100 a barrel, the Bank of America economists said oil costs would dampen consumer demand not only for gasoline but also for other goods and services. That level of energy prices is expected to shave two basis points from global growth in 2019.
"This is not a major impact, but it isn’t trivial either," they said. "Moreover, with oil supplies so tight any further disruption could mean a major spike in oil prices, creating more nonlinear impacts on confidence and growth."
On Monday, the International Monetary Fund lowered its global economic growth forecast for this year and next. The international lender cited in its report "rising trade barriers and a reversal of capital flows to emerging market economies with weaker fundamentals, and higher political risk."
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