The U.S Postal Service has signed five-year air cargo service agreements with seven airlines that will take effect on Sept. 30.The carriers that will participate in the contract are Dallas-based American Airlines Inc.; Houston-based Continental Airlines Inc.; Tempe, AZ-based US Airways Inc.; Forest Hills, NY-based JetBlue Airways; Oak Creek, WI-based Midwest Airlines; Indianapolis-based ATA Airlines Inc.; and Mendota Heights, MN-based Sun Country Airlines.