Southwest Airlines wants Denver travelers to leave Frontier and United behind and is willing to double the number of credits Rapid Rewards members earn for a limited time. Rapid Rewards members flying into or out of Denver between May 27 and Sept. 22, 2010 can earn one bonus credit on each one-way flight. Fly four roundtrip flights during the promotion and you can earn a total of 16 credits–enough for a roundtrip award flight. Passengers who purchase a Business Select Fare will earn 2.25 credits for shorthaul flights less than 750 miles and three credits on longhaul flights 750 miles or longer through Sept. 22, 2010. Registration at http://www.webflyer.com/link/?2644 is required prior to travel and the offer is valid on new reservations only. Bonus credits are not eligible for A-List qualification.