By David Bailey CHICAGO, April 18 (Reuters) - American Airlines said on Thursday it raised leisure air fares $20 round-trip systemwide, the second time in a week a major U.S. carrier sought an increase as the industry seeks to reverse huge losses following the Sept. 11 attacks. The increase by AMR Corp.'s (AMR) American Airlines hit public circulation Thursday afternoon, Bestfares.com Chief Executive Tom Parsons said. Other carriers may have matched the fares, but changes would not be available until late Thursday night or early Friday, he added. A spokesman for AMR, the world's largest air carrier, said the increase primarily affected leisure fares and was up to $20 per round-trip ticket. AMR reported a $575 million first-quarter net loss on Wednesday. Continental Airlines (CAL), the No. 5 U.S. carrier, led a similar bid to raise leisure fares last week. Most majors matched the increase, but the bid failed on Monday, after No. 4 U.S. carrier Northwest Airlines (NWAC) refused to go along. "You may still see some of the bigger airlines match quickly, but others may hold off until they see what Northwest is going to do," Parsons said. Northwest could not be reached immediately for comment. Delta Air Lines (DAL), the No. 3 U.S. carrier, also raised fares on many routes, one analyst said. Delta could not be reached immediately for comment. "Over the next couple of days we expect to get better clarity as to who will match and how extensive this fare action will be," Deutsche Bank Securities analyst Susan Donofrio wrote in a research note. Northwest may force the increase to be scaled back, but the attempts to increase fares suggest the industry has some confidence in forward bookings, Donofrio wrote. UAL Corp.'s (UAL) United Airlines raised fares $20 on scattered routes and fare types late on Wednesday. Northwest officials said Thursday they matched the increases on specific routes they believe could take an increase. No. 2 U.S. carrier UAL is scheduled to release first-quarter results on Friday. ©2002 Reuters Limited.