It’s one of 40 jets leased by Amazon.com Inc for a new cargo service to meet delivery demand from the retail giant’s customers. Exclusive payload data reviewed by Reuters and interviews with airport officials around the country show that Prime Air planes are flying nearly full, but with lightweight loads, taking away valued business from FedEx Corp and United Parcel Service Inc.

Expanding into transportation, from trucks to planes, is one of Amazon’s most important endeavors as it strives to lure new customers with fast shipping while keeping costs under control. The world’s largest online retailer is sending more packages, more often, and later in the day to serve its estimated 35 million to more than 50 million U.S. members of Amazon Pr…