With Trump’s announcement of US withdrawal from the agreement, the sanctions “effectively” went into place immediately. Steven Mnuchin, U.S. Treasury Secretary said that in a document accompanying the announcement, the Treasury Department gave an unequivocal “Yes” to the question of “Will the United States resume efforts to reduce Iran’s crude oil sales?”

Some oil traders had not expected such a harsh message.

According to Mnuchin, his “expectation is not that oil prices go higher.” He said that the U.S. has spoken to “various parties that would be willing to increase oil supply” to offset Iran. In fact, the Saudi state-owned press agency quoted an unnamed energy official as saying Riyadh would work “to mitigate the effects of any supply shortages” in the oil market.

Oil prices climbed throughout the previous week in anticipation of the withdrawal, but settled lower on Tuesday. U.S. West Texas Intermediate futures rose as much as 2.4 percent to $70.72 a barrel in New York and Brent in London climbed 2.5 percent to $76.75. Both are at the highest level since November 2014.

James Lucier and Tristan Berne of Capital Alpha Partners said in an emailed note that, “Countries that seek a ‘significant reduction’ waiver from the State Department in order to avoid secondary sanctions will need to demonstrate reductions in purchases by November 4th, so changes in buying patterns should be observed in the coming months.”

The U.S. Energy Information Administration claims that seven years ago, when the U.S. and its allies imposed additional sanctions on Iran because of its nuclear program, buyers in Europe and Asia switched to purchasing from Nigeria, Saudi Arabia, Kuwait, Iraq and Angola. As well, China increased its buying from Angola and Iraq, and other Asian countries imported from Nigeria.

An energy economist for Moody’s Analytics, Chris Lafakis, said in a statement, “The Iranian oil sanctions during the Obama era reduced Iranian crude oil production by 1 million barrels per day. The sanctions announced today are expected to result in a decline in Iranian crude oil production of 400,000 barrels per day. What made the multilateral sanctions enforced during the Obama era so effective was precisely the fact that they were multilateral, whereas President Trump’s sanctions are not.”

Saudi Arabia now has the ability to fill the gap, since it’s the member of OPEC with the most spare capacity. Following the last round of sanctions, Saudi Arabia boosted oil output in response to what it called “additional demand from customers.” In an interview with Bloomberg in April 2016, Crown Prince Mohammed bin Salman said that his country could raise output to 11.5 million barrels a day immediately.

It has been made clear that the U.S. will go after other nations doing business with Iran, and will specifically target reinsurance, which proved to be a particularly effective method of halting Iranian oil tankers in the past.

Additionally, the Treasury Department said it was keeping close track of “the quantity and percentage of the reduction in purchases of Iranian crude” during the 180-day wind-down period — especially for anyone seeking waivers to allow for some oil purchases.

Richard Nephew, senior research scholar at Columbia University’s Center on Global Energy Policy, said in a blog post, that Trump “directly threatened countries that refuse to cooperate with U.S. sanctions implementation.” He added, ”Notwithstanding the new guidance and mindful of decisions made regarding aluminum and steel tariffs, countries will likely reach out to the U.S. to seek clarification as to exactly what will be demanded of them and their companies.”