Analysts note that the fee is important not so much for its direct costs as for its signal: it increases the risk that shipping disruptions will lead to a supply shortage and wipe out surplus forecasts made earlier this month.

Andy Lipow, president of Lipow Oil Associates, told CNBC that the market had been expecting a supply increase following the memorandum signed between the US and Iran last month, but that optimism has faded.

"The surplus is definitely at risk, especially if the strait closes completely."

He estimates that if applied to crude oil, the fee would add about $16 to a barrel of oil transiting the strait, although the administration has not yet clarified the mechanism for imposing the fee. Citi warned that the imposition of the levy could also increase the likelihood of military conflict:

"The risks of military escalation have increased significantly if this announcement is implemented."

"The immediate impact is supportive of prices, but the more significant issue is the risk of further physical supply losses," said Henry Hoffman of the Catalyst Energy Infrastructure Fund.

WTI futures rose 2.75% to $80.30 per barrel, while Brent futures rose 2.80% to $85.65, following a 9.6% jump in the previous session.

The situation could be complicated if Asian demand recovers just as Middle Eastern supplies become less reliable, Hoffman added. Saudi Aramco recently cut prices by $11 per barrel, to a $1.50 discount to the Oman/Dubai benchmark, which should encourage Chinese refineries to increase purchases.