"Past mergers, United-Continental, Delta-Northwest, pointed to Southwest being the great price disciplinarian,'' said William Swelbar, research engineer with MIT's International Center for Air Transportation, who co-wrote the new airfare study. "It's not the disciplinarian that it was yesterday.'' The "Southwest effect" has been mentioned most recently in regard to the pending merger of US Airways and American Airlines. That combination, which would create the largest airline in the world, is currently on hold after the Department of Justice and attorneys general for six states and the District of Columbia filed a lawsuit to block it, claiming the union would lead to a loss of service and higher fares and fees for the traveling public. Southwest's entry into a market would often lead to fares coming down across the board, as other carriers dropped their prices to better compete with the low-cost giant. Some industry watchers have said that this leveling effect could help keep fares from skyrocketing despite a shrinking number of airlines left in the wake of Northwest and Delta merging in 2008, United and Continental linking up in 2010, and even Southwest's own merger with AirTran in 2011. Get the full story at USA Today