Updates share price in paragraph 3; adds Southwest and United's comments in paragraphs 10-11 and 18-22

By Rajesh Kumar Singh and Shivansh Tiwary

March 17 (Reuters) - U.S. airlines on Tuesday reported stronger-than-expected spring travel demand, supporting higher fares and revenue growth even as a surge in jet fuel prices linked to the Iran war pushed operating costs higher.

Executives said carriers were already using fare increases and capacity discipline to recover part of the added expense if elevated fuel prices persist.

Airline stocks rose, with Delta Air Lines DAL.N up about 7% in afternoon trade, while United Airlines UAL.O, American Airlines AAL.O, Southwest Airlines LUV.N, and Alaska Air ALK.N gained between 3% and 4%.

DEMAND STRENGTH LIFTS OUTLOOKS

Delta said consumer and corporate demand accelerated into March, prompting it to raise its first-quarter revenue forecast while maintaining its earnings outlook.

The Atlanta‑based carrier said sales over the past week rose about 25% from a year earlier, reflecting broad‑based strength across corporate travel, international routes, premium leisure and domestic main-cabin bookings.

"The story for us in this quarter is about revenue demand and the health of the demand set," Delta CEO Ed Bastian said at a J.P. Morgan industrial conference.

Delta now expects first-quarter revenue to grow at a high-single-digit percentage, compared with its earlier forecast of 5% to 7%.

American Airlines AAL.O said its first-quarter revenue is now expected to rise more than 10%, above its previous forecast of 7% to 10%, as demand outperformed expectations. The carrier now expects an adjusted loss per share at the low end of its prior 10–50 cent forecast range.

American CEO Robert Isom said revenue performance was improving faster than expected, with momentum extending into April and May. He said higher fuel prices had added about $400 million to the airline's first-quarter fuel bill since its last update seven weeks ago.

United said the first 10 weeks of the year were the strongest booking weeks in its history.

Southwest said demand strength was broad-based across business and leisure travel, with March on track to be its biggest corporate travel month on record. It maintained its outlook for significant margin expansion and earnings growth in 2026.

JetBlue JBLU.O said demand had strengthened across peak and off-peak periods and across premium and core cabins. Chief Executive Joanna Geraghty said a stable macro backdrop was still needed for sustained earnings in 2026.

Frontier Airlines ULCC.O, meanwhile, slightly narrowed its quarterly loss forecast, saying solid demand had helped offset higher fuel expenses.

FUEL COSTS TEST PRICING POWER

Jet fuel prices have jumped more than 50% since U.S. and Israeli strikes on Iran in late February, lifting costs for an industry where fuel is second only to labor and typically accounts for about 20% to 25% of total operating costs.

U.S. airlines are particularly exposed because most do not hedge fuel costs, unlike some European and Asian carriers that use hedging to cushion price shocks.

Bastian said jet fuel prices have "almost doubled since the start of the year," citing a $400 million increase in fuel costs in March alone.

He said the industry already had pushed through two fare increases in the past two weeks and that Delta remained well positioned to recover higher costs, with flexibility to cut capacity if fuel prices stay elevated.

AIRLINES BET DEMAND WILL HOLD

United said it was trying to make up for an estimated $4.6 billion jump in fuel costs this year through stronger revenue, but had also already cut some flying for May and June and was looking at more reductions.

Chief Executive Scott Kirby said the cuts were aimed at weaker flights, such as some midweek, Saturday and overnight services, and said the airline would rather leave some demand unmet than keep flying routes that lose money if fuel stays high.

Executives also argued that higher fares were not yet scaring customers away. United said fares booked over the past week were up 15% to 20%, while revenue from each seat flown in March was now expected to rise about 14%, up from about 8% at the end of February.

Kirby said airline fares have not kept pace with inflation since 2019, meaning carriers may still have room to raise prices without sharply hurting demand unless the broader economy weakens.

"At least as the environment sits today," he said, carriers could recover "100% of that increase in fuel price."

(Reporting by Rajesh Kumar Singh in Chicago and Shivansh Tiwary and Nathan Gomes in Bengaluru and Doyinsola Oladipo in New York; Editing by Sriraj Kalluvila, Nick Zieminski and Paul Simao)

((rajeshkumar.singh@thomsonreuters.com; +1-313-484-5370; Reuters Messaging: rajeshkumar.singh.thomsonreuters.com@reuters.net/))