(i) OBO (ore/bulk/oil) in 70,000 to 150,000 DWT range (ii) Oil/ore vessels in 150,000 to 250,000 DWT. They are designed so that they can carry bulk dry cargoes as well as oil and thus provide greater flexibility in operation. Some bulk trades are seasonal. Oil shipments are more frequent in winter than in summer. In such circumstances, the combination carrier can switch from one trade to another according to the respective trade requirements and the state of the freight market.