Jet fuel costs and supplies across the globe are under pressure from the US and Israeli war on Iran.

19 of the world's 20 largest airlines have cut flights in May, according to Cirium data.

Airlines have largely made cuts on routes with multiple daily flights or those with lower demand.

First, the Iran war made flights more expensive. Now, it's making them disappear.

All but one of the world's 20 largest airlines are reducing capacity in the coming months, according to aviation analytics firm Cirium.

Its analysis found the planned global capacity for May has dropped three percentage points since early March. Cirium revised its initial prediction of 4%-6% growth this year, saying it could decline by up to 3% under some potential scenarios.

The war has disrupted supply chains, trapping oil in storage facilities across the Middle East.

That saw the price of Brent crude oil rocket past $100 a barrel in early March, before dipping back below that benchmark once ceasefire talks began this month.

Jet fuel prices have risen even faster, doubling in price to almost $200 a barrel. And as the war drags on, jet fuel is getting harder to come by for countries that don't produce it or have limited supplies.

"In Europe, we have maybe six weeks or so (of) jet fuel left," the International Energy Agency's executive director, Fatih Birol, told the Associated Press on April 16.

Willie Walsh, the director general of the International Air Transport Association, an airline trade group, said the next day that "by the end of May we could start to see some cancellations in Europe for lack of jet fuel."

"This is already happening in parts of Asia," he added in the statement.

However, the European Union's transport commissioner, Apostolos Tzitzikostas, denied that the continent was close to running out of jet fuel.

"Any cancellations announced so far by European airlines are linked to the high cost of jet fuel, not to supply shortages," he added.

Several airlines have already canceled flights or grounded airplanes due to rising costs.

Here's a look at some of the airlines that have already started canceling flights due to rising prices and falling supplies.

Ryanair, Europe's largest airline, said it is considering reducing routes.

CEO Michael O'Leary said its jet fuel supply could be at risk if the war continues during an interview with Sky News.

"We don't expect any disruption until early May, but if the war continues, we do run the risk of supply disruptions in Europe in May and June," he said.

KLM said on April 17 that it was canceling 80 return flights from Amsterdam's Schiphol Airport, its main base.

It added that these routes were "no longer financially viable to operate" due to rising kerosene costs. The airline also clarified that there was no kerosene shortage.

The same day, Germany's Lufthansa announced that it was retiring dozens of aircraft ahead of schedule due to rising jet fuel prices and the impact of labor disputes.

Most of the airplanes are Canadair CRJ aircraft, as it shuts down its loss-making regional subsidiary Lufthansa CityLine.

Switzerland's Edelweiss Air also said it was canceling flights to the US, due to declining demand and rising fuel prices. It will no longer fly to Denver or Seattle, and will reduce the frequency of flights to Las Vegas.

A spokesperson for Scandinavian Airlines said that it would cut about 1,000 flights in April due to the surge in jet fuel costs.

They added that most of the canceled flights were on short-haul routes in the Nordic region, at airports with multiple daily flights.

And Aer Lingus said on April 20 that it had made adjustments to 2% of its schedule. In a statement, it said there were cancellations due to "mandatory maintenance on aircraft, along with a limited number of schedule adjustments."

The Irish Independent had previously reported that over 500 flights were being cut.

Several airlines in Asia said they would cut flights to mitigate fuel shortages and mounting costs.

Vietnam Airlines suspended seven domestic flight routes beginning April 1, a local state-run newspaper reported, according to Reuters. The outlet reported that Vietnam Airlines planned to slash flight volume by 10% to 20% a month over the next financial quarter if jet fuel prices rise to $160 to $200 per barrel.

Other local airlines, including Vietjet Air and Bamboo Airways, will also cut flights.

AirAsia said it has cut 10% of its flights and raised fares to curb the impact of rising fuel costs. The Malaysian low-cost carrier, which flies to 25 countries, added that it would cut capacity on routes where it couldn't cover fuel costs.

At a media briefing on April 6, CEO Bo Lingam said the fuel surcharge has risen up to 20%, and overall ticket prices have risen 30% to 40%.

Lingam said its jet fuel had risen from $90 per barrel before the war to $200 per barrel, describing this as the airline's most serious challenge.

United Airlines CEO Scott Kirby said in a March memo to staff that the company would cut flights over the next two quarters.

"In the short term, that means tactically pruning flying that's temporarily unprofitable in the face of high oil prices," Kirby said.

The airline planned to cancel some off-peak flights and red-eyes.

"If prices stayed at this level, it would mean an extra $11 billion in annual expense just for jet fuel," Kirby said in a message to employees posted on the company's website. "For perspective, in United's best year ever, we made less than $5B."

Delta hasn't officially announced any flight cuts due to fuel prices; the oil refinery it owns in Pennsylvania has given it a buffer during the crisis.

"It's not going to cover the crack entirely, but gives us a fairly significant hedge," Delta CEO Ed Bastian said at a March JP Morgan conference.

Delta is cutting its seasonal Los Angeles to Anchorage route this summer, telling Business Insider that it "adjusts its schedule to align with customer demand." Alaska Airlines will be the sole operator on that route.

Air New Zealand said it would cut about 5% its flights, or about 1,100, at the start of May.

"We're focused on consolidating flights that are off-peak flying hours, for example, or where there is an alternative that we can re-accommodate customers," CEO Nikhil Ravishankar told 1News, a local outlet, in March.

Air Canada said it will suspend certain routes starting in late May due to rising jet fuel costs.

"Jet fuel prices have doubled since the start of the Iran conflict, affecting some lower profitability routes and flights which now are no longer economically feasible," the company's statement said. "Schedule adjustments including some frequency reductions are being made in response."

The route suspensions will impact certain domestic Canadian, transborder, and international flights.

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