This is true. I've often seen them more expensive - sometimes by a couple hundred dollars. They also leverage behavioral economics - people irrationally overvalue things that are free, thus the promotion of "bags fly free". It's not hard to do the math on bag checks, but that adds $60/bag/flight for people who rarely fly and don't have status on an airline. It also helps eliminate the time and chaos of finding overhead space on the plane and taking bags off to gate check them, which helps with being on-time (but weather and runway delays are the biggest cause of not being on-time). That being said, I just looked at prices going from Chicago to Austin, TX, over Memorial Day. For direct routes with similar flight times, Southwest came in at $300 whereas United came in at $360. This factors in what it costs to not get a middle seat (regular economy on United, paying $20/flight on Southwest for automatic early check-in). If I switch the destination to Denver, similar parameters (direct flights, no middle seat), it comes to $366 for United and $265 for Southwest. However, if I switch to Labor Day weekend, United is $168 to Denver or Austin, Southwest is $319 to Denver and $200 to Austin.