U.S. airlines face an “existential threat” from a surge in jet fuel that may drive their costs dramatically higher, according to Deutsche Bank.

Jet fuel prices in the U.S. have surged during the war in the Middle East — more than doubling on a year-to-date basis while crude oil advanced by about 50% in the same period. The last time that kind of widening in the so-called crack spread, the difference between underlying oil prices and jet fuel prices, happened was in 2005, the firm wrote in a March 6 note to clients, adding that back then “the damage to the airline industry was significant and widespread,” with carriers Delta Air Lines and Northwest Airlines filing for bankruptcy.

“Some of the industry’s financially weakest carriers could halt operations,” analyst Michael Linenberg wrote. “Absent near-term relief, airlines around the world could be forced to ground thousands of aircraft.”

Airline stocks extended a slide on March 6 alongside other travel and logistics companies. A gauge of the group is down 19% across six trading sessions, heading for its worst stretch since April.

Deutsche Bank is the latest firm to sound the alarm about the impact that the escalating conflict in Iran will have on airlines. 

American Airlines Group Inc. saw its stock downgraded earlier in March at Rothschild & Co. Redburn, which now expects the carrier to lose money this year as it pays more for fuel.