Freight transportation is carried by a variety of networks. The largest percentage of US freight is carried by trucks (60%), followed by pipelines (18%), rail (10%), ship (8%), and air (0.01%).[9] Other modes of transportation, such as parcels and intermodal freight accounted for about 3% of the remainder. Air freight is commonly used only for perishables and premium express shipments. The difference in percentage of rail's share by ton-miles and by weight (10% vs 38%) is accounted for by the extreme efficiency of trains. A single railroad locomotive may pull fifty boxcars full of freight while a truck only pulls one. Trucks surpass trains in the weight category due their greater numbers, while trains surpass trucks in the ton-miles category due to the vast distances they travel carrying large amounts of freight.
Usually cargo, apart from petroleum and other bulk commodities, is imported in containers through seaports, then distributed by road and rail. The quasi-governmental United States Postal Service has a monopoly on letter delivery (except for express services) but several large private companies such as FedEx and UPS compete in the package and cargo delivery market.