Shipping lines and cargo owners effectively use containers to import goods from abroad. Once the containers arrive at port, there is a set time allowed for the cargo owner to return the empty containers to a certain depot, rail terminal, or other location. If the containers are returned past the last free day, they begin accruing fees or charges known as container per diem for each day past the free period. The per diem charges will vary depending on the equipment, its location, and the duration of the delay. However, fees are assessed daily until the container is returned to the equipment owner.