If the U.S.-Israel war on Iran continues into the summer, then airlines will start running out of jet fuel and will be forced to trim flights, according to Ryanair CEO Michael O’Leary.

In an interview Thursday with the U.K.’s ITV News, he said carriers will be in an “unknown scenario” if the Strait of Hormuz stays closed for two to three more months, warning 5%-10% of flights in May, June, and July might have to be canceled.

By that point, O’Leary added airlines won’t be able to choose which flights to cancel, explaining that they will get little advance notice and it would depend on how much jet fuel each airport still has available.

“So we will then look around, and we will be trying to ground one or two aircraft and minimize the inconvenience for customers,” he said. “But it’s going to be difficult. It’s going to be challenging.”

Despite the risk of cancellations, O’Leary said he would “strongly advise” that anyone planning a trip this summer book as soon as possible, before airfares get pricier.

In fact, jet fuel prices have soared even higher than gasoline prices have as the Iran war has not only bottled up one-fifth of the world’s oil supply but a big chunk of the refining capacity that churns out jet fuel.

The U.S isn’t immune either, and top airport hubs like Chicago, Houston, Los Angeles and New York have seen the average price for a gallon of jet fuel hit $4.88 per gallon, nearly double compared to the prewar price.

As a result, more airlines are hiking fees for checking luggage, and United Airlines is bracing for a prolonged war that sends oil as high as $175 a barrel and is making contingency plans that include reducing capacity.

When asked if booking a flight now would be a gamble given the possibility that a flight may not exist this summer, O’Leary replied he doesn’t think so.

“Life is a gamble,” he added. “I think we’re looking at maybe the risk to 5 or 10% of cancellations in June or July, but 95-90% of flight will still operate. So I think you’re really not taking much of a gamble. I would be much more concerned if you delay your booking, that actually you and your family will be paying much higher prices.”

O’Leary acknowledged that travelers who face canceled trips wouldn’t be able to get refunded as airlines could claim circumstances beyond their control.

But he pointed out anyone flying within Europe won’t be stranded and is entitled to have airlines reroute a trip or get them back home.

“At Ryanair, we have lots of flights on a daily basis. We will re-accommodate you, get you back, get you out, whatever it’s going to be,” O’Leary vowed. “You might be stuck for a day or two. But if you’re staying within Europe, you should be reasonably confident that, A, your original flight will operate and, B, if there is a disruption, bear in mind there’ll be far more disruptions this summer from French air traffic controllers not showing up to work.”

This story was originally featured on Fortune.com