For several years the only airline service was from Northwest Airlines, commuter service on Northwest Airlink to Minneapolis–Saint Paul International Airport. In October 2007, Frontier Airlines began service with two daily flights between its Denver hub and Sioux City. The new service from Frontier quickly expanded to three daily non-stop flights to Denver and helped passenger traffic increase by over 150%. In April 2008, Frontier announced it would be ending service to Sioux City on May 12, citing economic conditions after the company filed for Chapter 11 bankruptcy.