CHICAGO, April 19 Reuters U.S. airlines have enjoyed a travel boom for the past three years, but until this past quarter, bigspending 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  all reported a sharp rebound in flying for business purposes.

On Thursday, Alaska Air said increased spending by technology companies like Amazon.com and Microsoft in the March quarter increased revenue from corporate travel to prepandemic levels. For most of the last year, the carrier39;s business bookings were stuck around 75 of the 2019 levels.

The corporate travel increase helped the Seattlebased carrier post a strong performance in the March quarter, traditionally its weakest period of the year.

In an interview, Alaska39;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…