Oil products tankers are non-specialised tankers below 60,000 dwt, as well as coated tankers above this size. These ships carry a spectrum of cargoes, ranging from relatively unsophisticated dirty products such as fuel oil through to clean products such as naphtha. Vessels that trade at one end of this spectrum are unlikely to be able to switch easily to the other end, and "last cargo" regulations ensure that dedicated fleets become established for some cargo types. At the most sophisticated end of the fleet there is an overlap with the chemical sector, with a significant volume of "swing tonnage" that can operate in either