American travelers could be facing one of the most expensive summers for European vacations ever as airlines slash thousands of flights, add surcharges to transatlantic routes and hike prices.

It all comes down to Europe’s jet fuel supply, about 40% of which passes through the Strait of Hormuz. The crucial trade route has been blocked off due to the Iran war, more than doubling fuel costs for European airlines.

“There are alarms going off across Europe right now. It is considered critically low,” Joe Adamski, managing director of ProcureAbility, a supply chain consultancy, told The Post. 

The average airfare for a trip to London hit $1,151 last week – up nearly 40% from $826 last year, according to data from Kayak, which tracks weekly flight searches.

Flights to Rome are 32% higher, averaging $1,066, and trips to Paris cost 28% more this year, or about $1,091 – and the travel season is yet to hit its traditional peak.

“June and July are the most expensive,” said Brian Kelly, founder of travel website “The Points Guy,” advising tourists to book trips now for late August and September if they’re looking for deals.

“Even if a deal [to end the war] is reached today, it’s gonna be six to eight weeks before there’s meaningful supplies making it to Europe … so the chances are very low that this summer we’re going to see a steady drop in airline pricing.”

After paying $1,000 or more for a flight, tourists might find themselves facing exorbitant prices abroad, said Kelly — who actually suggested Americans look elsewhere for travel destinations this year.

Fewer Europeans are making long-distance trips due to conflicts in the Middle East, as well as concerns about US immigration policy, Kelly said. That means more Europeans will be vacationing closer to home, raising demand – and prices – for hotels and other services.

The US dollar is also weak compared to the eurozone’s currency – with an exchange rate of $1.17 per euro – so Americans won’t get as much bang for their buck on the continent, added Kelly.

Along with quietly raising ticket prices, many airlines have started adding surcharges and raising checked bag fees to cover higher jet fuel costs, which typically land among carriers’ biggest operating expenses.

Air France and KLM, which is based in the Netherlands, doubled their fuel surcharge on long-haul flights from 50 euros to 100 euros, or about $58 to $116. 

Transatlantic flights will face an additional surcharge of 70 euros, or about $80 – meaning Americans looking to fly abroad will need to shell out nearly $200 in extra fees.

Virgin Atlantic has hiked some ticket fares by anywhere from 50 euros to 360 euros, or about $58 to $418, depending on cabin class – and the England-based carrier’s CEO has warned that more price hikes could be on the way.

Flight cancellations are also a concern, since long-haul routes – like those between the US and Europe – are usually first on the chopping block because they guzzle up the most fuel.

Norse Atlantic Airways, a Norwegian airline, canceled flights to LAX in April – including trips between Los Angeles and London – citing jet fuel concerns.

The Lufthansa Group, a German company that owns Lufthansa Airlines, Austrian Airlines and Brussels Airlines, also announced last month that it would cut 20,000 short-haul flights through October as a result of the war’s supply disruptions. Cancellations will largely hit the company’s hubs in the German cities of Frankfurt and Munich.

Despite intense pressure on their supply chains, airlines aren’t warning about fuel shortages yet.

“The fuel is still there,” Adamski told The Post. “The concern is how little fuel there is, and they are canceling flights in anticipation of those disruptions in order to conserve what is there.”

He estimated the EU is down to a 21-day fuel supply, already below its typical low of 30 days during peak summer travel — and that’s “a scary low number for them. There’s no quick way to recover that.”

The US is on somewhat more stable footing, with about 45 days’ worth of supply – though that’s still significantly lower than the typical 105- to 150-day supply, Adamski said.

“US airlines could remain robust through the fall,” Jeff Krimmel, founder of Krimmel Strategy Group, told The Post. “You would need probably another four to six months of war for US airlines to become sufficiently distressed.”

So far, “there has been a general surprise of how robust the travel segment of the economy has been relative to these [price] increases,” he said.

It’s likely further evidence of the so-called K-shaped economy, or the idea that low-income consumers are hit harder by inflation while more affluent individuals – the main customer base for airlines – are benefiting from stock market gains and higher wages, Krimmel added.

The real concern is whether supply disruptions will last until the winter, when limited refining capacities will be split between the need for jet fuel and heating oil – potentially further reducing supply, according to experts.