Oil prices soared, registering their most significant single-day gain since April, after former U.S. President Donald Trump announced plans to reimpose a blockade on Iranian vessels transiting the Strait of Hormuz and to impose a fee on all other cargo moving through the critical waterway, dashing recent market hopes for a swift recovery in shipping flows.

The WTI futures contract surged by 9.4%, settling near $78 per barrel, its highest level in approximately a month. Brent crude closed above $83. These moves reinforced the bullish momentum in oil prices, following weekend strikes between the U.S. and Iran, including attacks on energy infrastructure, which had largely extinguished hopes that mid-June tensions would ease and allow normal transit through the strait to resume.

In a social media post, Trump stated that the Strait of Hormuz "will remain open with or without Iran," declaring that Washington would become the "guardian" of the passage. He also demanded a 20% compensation fee on all other cargo shipped through Hormuz. Earlier, he had suggested to Fox News that the U.S. might seek to take control of this strategic chokepoint.

"Reinstating the blockade is another step in the escalation, forcing crude to reprice geopolitical risk," said Rebecca Babin, senior energy trader at CIBC Private Wealth Group. "The proposed 20% toll is eye-catching, but the market is still waiting to see how it would be implemented, who bears the cost, and how other Gulf oil producers will respond."

More than a dozen shipping market participants expressed surprise and confusion over Trump's announcement of a potential fee on cargo passing through the strait. Several of these individuals have had vessels transit the Strait of Hormuz in recent weeks. They indicated it is currently impossible to judge what the plan would actually entail or how it might influence their transit decisions.

The White House did not provide further details on Trump's toll proposal, including how it would be enforced or whether U.S. allies in the Gulf region had been informed.

Concurrently, the Combined Maritime Information Centre stated that U.S. Central Command would begin enforcing a blockade on all Iranian ports and coastal areas starting at 4 p.m. Eastern Time on Tuesday.

Analysts warned that re-establishing a blockade could prompt Iran to increase attacks on vessels attempting to pass through the Strait of Hormuz. Vessel-tracking data compiled by Bloomberg showed the number of ships transiting the strait on Sunday fell to a one-month low, though many vessels pass through the waterway with their satellite signals turned off.

Calculated at current oil prices, a 20% fee would equate to approximately $32 million for a Very Large Crude Carrier. This far exceeds the previously reported maximum fee of around $2 million charged by Iran, according to informed sources. The resulting higher shipping costs would likely be reflected in oil prices.

In a related development, Yemen's Houthi group stated on Monday it had launched multiple ballistic missiles and drones at an airport in Saudi Arabia, describing the attack as a response to a prior Saudi strike on Sana'a International Airport.

Saul Kavonic, a senior energy analyst at MST Marquee, noted that oil prices could approach $100 per barrel if the conflict broadens to more extensively target critical infrastructure.

In New York, the WTI August futures contract rose 9.4% to settle at $78.14 per barrel.

The Brent September futures contract gained 9.6%, settling at $83.30 per barrel.