A ship constructed or adapted primarily to carry oil in bulk in its cargo spaces. This includes combination carrier and any chemical tanker when they carry a cargo or part cargo of oil in bulk.
Beam and draft restriction have led to a few preferred sizes of oil tankers:
About 35,000-45,000dwt: Panamax tankers configured for transit through the Panama Canal when loaded to their design draft.
About 70,000-120,000dwt: Aframax tankers.
About 120,000-165,000dwt: Suezmax tankers, they may be arranged for multiple grades (three segregated grades is common).
About 200,000-310,000dwt: Very Large Crude Carriers (VLCC) designed for the carriage of crude oils on longer voyages.
About 310,000-550,000dwt: Ultra Large Crude Carriers (ULCC).