President Donald Trump signed a 90-day extension of the Jones Act waiver on Friday, two days before the current waiver was set to expire, allowing foreign-built and foreign-crewed ships to keep moving goods between U.S. ports in the administration's push to hold down fuel costs.

The Jones Act, a century-old shipping law, requires that all goods transported between U.S. ports travel on vessels that are U.S.-built, U.S.-flagged and U.S.-crewed. The administration first suspended that requirement in March, shortly after the start of the war in Iran sent global fuel prices soaring. The waiver is designed to minimize disruptions to fuel transportation and give the shipping industry greater flexibility.

The extension is now the longest waiver in the law's history.

How much cargo has moved under the waiver?

A White House official told the Washington Examiner that since the waiver took effect, an additional 90 million barrels of products have been shipped between U.S. ports. The breakdown:

• 27 million barrels of gasoline
• 26 million barrels of crude oil
• 6 million barrels of renewable fuels

That is roughly 1 million barrels per day of coastal cargo moved without Jones Act-compliant vessels.

What does the extension mean for pump prices?

As of Friday, the national average price of gasoline stood at $3.87 per gallon, and diesel at $6.06 a gallon, according to AAA.

GasBuddy analyst Patrick De Haan said earlier this month that the Jones Act waiver has been one of the most significant factors keeping prices from climbing higher.

"If it wasn't for the Jones Act waiver, I would say that gas prices and diesel would be quite a bit more elevated," De Haan said.

He added: "The Jones Act has been really a lifeline for the shipment of gasoline, diesel, jet fuel, etc. For those shipments to go where they need to because without the Jones Act waiver, you have to find a U.S. crew at a much higher price and only a certain amount of vessels are U.S. vessels that meet the Jones Act."

The constraint is structural. Only a limited number of U.S.-built, U.S.-crewed vessels qualify under the law, and crewing them costs far more than foreign-flagged alternatives.

Why now?

The wars in Iran and Ukraine have crimped the global fuel supply chain, with shipments through the Strait of Hormuz remaining constrained. Ahead of the midterm elections, the Trump administration has taken multiple steps to lower gas and diesel prices:

• Allowing greater access to red-dyed diesel
• Encouraging state-level gas tax suspensions
• Striking a deal with Russia for fuel supplies

Who opposes the waiver?

Some lawmakers and domestic shipping industry groups have rallied against extending the waiver, arguing the law exists to protect American shippers and the U.S. maritime industrial base.

The American Maritime Partnership, an industry coalition, said in a statement on Friday that it "calls for a prompt end to the waiver and looks forward to working with the Administration to advance our shared goal of restoring American maritime dominance by unleashing investment in rebuilding and growing the U.S. domestic fleet."

The group's objection puts it at odds with fuel-price hawks inside the administration, who credit the waiver with preventing steeper increases at the pump.

The 90-day clock now runs into the fall, setting up the next decision point as midterm elections approach.