A potential US ban on diesel exports would slash domestic prices for the fuel at the outset, but the effect is likely to be short-lived, according to executives, traders and analysts. A 30-day halt on US overseas shipments combined with an existing waiver of the Jones Act “could work surprisingly well, at least initially,” JPMorgan Chase & Co. analysts including Natasha Kaneva wrote in a note to clients Thursday. Retail diesel prices would tumble to $4.70 a gallon within 15 days from record highs above $6.50 a gallon, the analysts said.

But the situation would degrade quickly after that point, the analysts warned. The economics would quickly make storage less attractive and squeeze profits, likely pushing refiners to process fewer barrels of crude oil and make less fuel of all kinds. As war in Iran, Russia and Ukraine squeezes diesel supply, the Trump administration is mulling ways to tame prices ahead of the November midterm elections.

A ban on US exports would hit some of the country’s key allies, including Brazil and the United Kingdom. While President Donald Trump said he’s encouraged his advisers to support an export ban, the White House denied a Politico report that it’s weighing a 90-day halt. Energy Secretary Chris Wright said the administration was looking to help the industry independently boost diesel supplies even in the absence of a government ban.

Calculating how long an export ban would cut domestic diesel prices is tricky. Some industry observers forecast that refilling US storage could take longer than the 30 days estimated by JPMorgan. On the Gulf Coast, it would likely take only four to eight weeks for storage to fill, according to Steven Barsamian, chief operating officer of The Tank Tiger.