Ryanair, the Irish low-cost airline, has reported a 15% fall in half-year profits after the price of the fuel it had not locked in doubled.
Profit after tax fell to €2.15 billion in the six months to the end of September, down from €2.54 billion a year earlier.
The airline also warned that its fuel bill could rise by about €2 billion in the next financial year, based on current prices.
Ryanair said higher fares were unlikely to cover the full increase, and it is reviewing costs across the group.
Michael O'Leary, chief executive, said this could include temporary pay freezes, fewer crew per aircraft and greater use of artificial intelligence (AI) in back-office work.
Ryanair has hedged 80% of its fuel for the current year at about $67 a barrel, meaning it agreed the price in advance.
The remaining 20% doubled in price to about $130 a barrel, which pushed operating costs up 10% to €7.69 billion.
Only 25% of next year's fuel is hedged, at about $95 a barrel.
Passenger numbers rose 6% to 125.8 million, but average fares fell 4% to €55.70.
O'Leary blamed the lower fares on conflict in the Middle East, which made customers hesitant and pushed them to book later.
Revenue rose 3% to €10.08 billion.
Ryanair has already cut its passenger target for the year from 216 million to 214 million to reduce its exposure to unhedged fuel.
It declined to give full-year profit guidance, saying it had little visibility of bookings beyond Christmas.
Fares for the October to December quarter are running slightly ahead of last year.
The airline declared an interim dividend of €0.273 a share and announced an €800 million share buyback, starting in February.
Ryanair expects to take delivery of its first 16 Boeing 737 MAX-10 aircraft next spring and plans to grow traffic to more than 220 million passengers next year.
