CHICAGO, April 19 (Reuters) - U.S. airlines have enjoyed

a travel boom for the past three years, but until this past

quarter, big-spending corporate travelers had been largely

missing.

Those customers are now back in full force, boosting profits

for carriers in what is normally a weak quarter for results. The

U.S. airlines that have so far released results - including

Delta, United and Alaska Air ( ALK ) - all

reported a sharp rebound in flying for business purposes.

On Thursday, Alaska Air ( ALK ) said increased spending by

technology companies like Amazon.com ( AMZN ) and Microsoft ( MSFT )

in the March quarter increased revenue from corporate

travel to pre-pandemic levels. For most of the last year, the

carrier's business bookings were stuck around 75% of the 2019

levels.

The corporate travel increase helped the Seattle-based

carrier post a strong performance in the March quarter,

traditionally its weakest period of the year.

In an interview, Alaska's chief financial officer, Shane

Tackett, said demand would keep growing, as spending by

technology companies has not fully recovered.

"Technology companies on the West Coast are the most

valuable companies in the world," he said. "They are going to

travel to see their customers and to sell software."

Similarly, United said it recorded some of the biggest

corporate bookings in its history this year, thanks to demand

from professional services, tech and industrial companies.

Business trips generated as much as half of passenger

revenue at U.S. airlines before the global health crisis,

according to industry group Airlines for America.

But the sluggish recovery forced carriers dependent on

business traffic to rework their network and chase vacationers.

Pricing power fell due to excess industry capacity in key

leisure markets.

United shifted more seats to markets like Florida and Las

Vegas in the first quarter following losses in the same quarter

last year, while American Airlines ( AAL ) reset the terms of

its contract with big corporate customers.

While the pickup in business travel is largely linked to

people returning to offices, airline executives say corporate

clients are loosening their purse strings due to the improved

economic outlook.

Delta last week said 90% of its corporate customers are

planning to either maintain or increase travel volumes in the

current quarter. The Atlanta-based airline, which saw a

double-digit year-on-year increase in corporate sales in the

first quarter, expects to deliver record corporate revenue in

the second half of this year.

Alaska raised its 2024 earnings forecast as it expects

profit from business travelers to offset higher fuel costs.

United's chief financial officer, Michael Leskinen, on

Wednesday said the recovery in business traffic was "wind in our

sails," saying that while current trends were strong, "the

future is even brighter."