Southwest shares closed up 19% on Thursday, their biggest daily gain in nearly half a century. Despite some initial friction from the flying (and posting) public, Southwest Airlines is feeling pretty bullish about its recent revenue-boosting initiatives like bag fees and premium seating options. Driving those profits are low-cost, high-reward changes like bag fees, which Southwest earlier this year said would bring in more than $350 million in 2025, tracking at $1 billion annualized. On its Thursday earnings call, Southwest highlighted another byproduct of its new fees. “We are not seeing book away from Southwest Airlines.