In 1926 the U.S. Postal Service began selling its airmail routes to private carriers. In May 1927 Boeing won the bidding for the San Francisco-to-Chicago airmail route with a bid of $2.89 per pound of mail — half of what it cost the Postal Service to fly it. Boeing was able to offer a lower bid based on the performance of a brand new Boeing plane, the Model 40A. The Model 40A was the company's first successful commercial aircraft; was more economical to operate and could carry more mail and passengers than its competitors. The biplane had a crew of one, a compartment for and a small cabin for two passengers. Boeing built 25 of the model 40As and delivered all of them within 40 days.