This company started in 1924 as a fleet of crop dusting planes, and began operations as a commercial airline in 1929. At present the oldest airline still operating in United States, Delta was in trouble in the mid-2000s. Squeezed by higher fuel prices and disrupters like JetBlue and Southwest, it was forced to file for bankruptcy in April 2007. Apart from merging with Northwestern Airlines, Delta renegotiated union contracts and expanded its fleet with used planes instead of costly new ones. Delta once again took flight and in 2013, 120.4 million passengers boarded Delta planes—more than any other airline.