Airlines trying to claw their way out of two bruising pandemic years are now facing the most expensive jet fuel costs in more than 13 years.

Russia’s invasion of Ukraine last month has set off a global panic around fuel supplies. Now, some analysts expect U.S. carriers to trim first-quarter profit and revenue estimates in the coming weeks after fuel costs rose 32% last week alone. The expense is generally airlines’ second biggest, behind labor.

“The higher fuel will more than wipe out better revenue near-term resulting in modest reductions to 1Q22 estimates,” wrote MKM Partners airline analyst Conor Cunningham in a note.

The surge in fuel prices — more than 50% so far this year — is the latest challenge for carriers that expect travelers to come back in droves this year as Covid-19 cases fall.

Airline stocks have been among the hardest-hit industries in recent weeks as Russia’s invasion threw markets into turmoil.

United Airlines, which has the biggest international network of the U.S. carriers, was down more than 10% in early-afternoon trading on Monday, trading at its lowest levels since November 2020. Delta Air Lines fell more than 8% and American Airlines dropped 7%. The S&P 500, in comparison, is down 2% so far on Monday.

Airlines are limited in how much they can trim capacity to raise fares as they chase passengers returning to the skies.

For the second quarter, U.S. domestic schedules are flat compared with 2019 “and we doubt much capacity will be cut given the increased competition for the leisure customer,” Andrew Didora, Bank of America airline analyst, said in a Monday research note.

Didora said travel demand should outpace supply, particularly during peak leisure times, “but it will not create nearly enough pricing to offset the fuel move.”

The second and third quarters, which coincide with spring and summer vacations, are when U.S. carriers generate the bulk of their revenue.

It could take months before travelers feel the fuel price in tickets. Cowen & Co. airline analyst Helane Becker sees a roughly four-month delay before fares catch up.

“As a result, it is likely the next few months will be financially concerning, even though traffic is strong,” she said in a note Friday.

Some large U.S. airlines like American abandoned fuel hedging after oil prices peaked and then crumbled in 2014. The fuel-price slump drove a decade of U.S. airline profits that was eventually upended by the coronavirus in 2020.

“It’s not something we’re considering at this time,” American spokesman Matt Miller said about hedging.

United and Delta, which owns a refinery, didn’t immediately comment.

United’s “current strategy is to not enter into financial transactions to hedge the market price exposure of its expected fuel consumption, although the Company regularly reviews its strategy based on market conditions and other factors,” it said in its annual report last month.

MKM Partners’ Cunningham told CNBC that airlines not currently hedging fuel prices may have missed the boat — prices are already high just at a time when they’re trying to keep a lid on costs.

“If someone was to announce hedging today, I think that stock would get obliterated,” he said.