Frontier's service was replaced by Pioneer Airlines Swearingen Metroliners nonstop to Denver, code sharing flights as Continental Express for Continental Airlines. By 1989 Continental Express nonstops to Denver were Rocky Mountain Airways ATR 42s and Beechcraft 1900Cs. In 1995 the Continental Express code share service at the airport was being operated by GP Express Airlines with Beechcraft 1900Cs nonstop to Denver. By 1991 United Express (Mesa Airlines) had joined Continental Express at the airport with Beechcraft 1900Cs nonstop to Denver flown via a code sharing agreement with United Airlines. Continental shut down its hub in Denver and by 1999 only United Express (Great Lakes Airlines) served the airport, with nonstop Beechcraft 1900s to Denver. Great Lakes later lost its United Express designation but continued to serve the airport as an independent airline before dropping Riverton.