Bulk carriers transport materials such as coal, minerals and grains. They usually operate under a nonscheduled or tramp service, whereby the purchaser of the cargo charters a vessel and then works out a route and sailing time with the shipping company. Buyers shipping ordinary commodities use vessels which carry many large square containers.
散裝船是運送大宗物資如煤、礦砂、穀物的船隻，多由貨主談妥購買合約後，再尋找航商託運，屬於不定期船。