Even more than container traffic, transport flows in the bulk sector are usually subject to directional imbalance. Mineral resources are often geographically distant from where they are processed. Large ore and coal freighters and crude oil tankers are therefore only transporting cargo in one direction, from the port of shipment to the port of discharge. They usually return empty. In many cases, therefore, the freight rate must cover the costs of returning the empty ship. This partially explains the great disparity of freight rates on individual routes depending on direction.