Southwest Airlines is looking to add smaller cities to its domestic route network before expanding overseas, CEO Gary Kelly said in a conference call on Thursday. "[B]y definition, the majority of [new cities] are going to be relatively small compared to our overall route network," Kelly said, explaining recent choices such as Panama City, Fla., and Greenville-Spartanburg, S.C. "There are new customers to win in those new cities." Kelly also said the airline is talking to Boeing about a replacement for the 737, which makes up Southwest's entire fleet. "We are in need of a more efficient, cost-effective aircraft; that's our mission," he said. "And we're obviously very hopeful that Boeing can meet our needs."