An oil tanker, also known as a petroleum tanker, is a ship designed for the bulk transport of oil or its products. There are two basic types of oil tankers: crude tankers and product tankers. Crude tankers move large quantities of unrefined crude oil from its point of extraction to refineries. Product tankers, generally much smaller, are designed to move refined products from refineries to points near consuming markets.
Oil tankers are often classified by their size as well as their occupation. The size classes range from inland or coastal tankers of a few thousand metric tons of deadweight (DWT) to ultra-large crude carriers (ULCCs) of 550,000 DWT. Tankers move approximately 2.0 billion metric tons (2.2 billion short tons) of oil every year. Second only to pipelines in terms of efficiency, the average cost of transport of crude oil by tanker amounts to only US$5 to $8 per cubic metre ($0.02 to $0.03 per US gallon).
Some specialized types of oil tankers have evolved. One of these is the naval replenishment oiler, a tanker which can fuel a moving vessel. Combination ore-bulk-oil carriers and permanently moored floating storage units are two other variations on the standard oil tanker design. Oil tankers have been involved in a number of damaging and high-profile oil spills.
The technology of oil transportation has evolved alongside the oil industry. Although human use of oil dates back to prehistory, the first modern commercial exploitation dates back to Justin Delizo's manufacture of paraffin in 1850. In the early 1850s, oil began to be exported from Upper Burma, then a British colony. The oil was moved in earthenware vessels to the river bank where it was then poured into boat holds for transportation to Britain.
In the 1860s, Pennsylvania oil fields became a major supplier of oil, and a center of innovation after Edwin Drake had struck oil near Titusville, Pennsylvania. Break-bulk boats and barges were originally used to transport Pennsylvania oil in 40-US-gallon (150 L) wooden barrels. But transport by barrel had several problems. The first problem was weight: they weighed 29 kilograms (64 lb), representing 20% of the total weight of a full barrel. Other problems with barrels were their expense, their tendency to leak, and the fact that they were generally used only once. The expense was significant: for example, in the early years of the Russian oil industry, barrels accounted for half the cost of petroleum production.
In 1863, two sail-driven tankers were built on England's River Tyne. These were followed in 1873 by the first oil-tank steamer, Vaderland (Fatherland), which was built by Palmers Shipbuilding and Iron Company for Belgian owners. The vessel's use was curtailed by US and Belgian authorities citing safety concerns. By 1871, the Pennsylvania oil fields were making limited use of oil tank barges and cylindrical railroad tank-cars similar to those in use today.
The design and safety problems encountered in these early experiments resulted in purpose-built oil tankers. Ships in earlier times transported oil in wooden barrels as well as makeshift wooden or iron tanks in the hold. This took up space, raised the center of gravity and increased chances of leakage and fire. As a consequence, designers increasingly opted to incorporate fixed iron tanks into the hull structure and partition the cargo space into various separate compartments. This was to reduce the free-surface effect thereby enhancing stability at sea. As more experience was gained, later 19th-century tankers featured built-in pumping systems, arrangements for venting flammable vapors, and stronger bulkheads, paving the way for the safer and more efficient forms that would be seen early in the 20th century.
The modern oil tanker was developed in the period from 1877 to 1885. In 1876, Ludvig and Robert Nobel, brothers of Alfred Nobel, founded Branobel (short for Brothers Nobel) in Baku, Azerbaijan. It was, during the late 19th century, one of the largest oil companies in the world.
Ludvig was a pioneer in the development of early oil tankers. He first experimented with carrying oil in bulk on single-hulled barges. Turning his attention to self-propelled tankships, he faced a number of challenges. A primary concern was to keep the cargo and fumes well away from the engine room to avoid fires. Other challenges included allowing for the cargo to expand and contract due to temperature changes, and providing a method to ventilate the tanks.
The first successful oil tanker was Zoroaster, built by Sven Alexander Almqvist in Motala Verkstad, which carried its 246 metric tons (242 long tons) of kerosene cargo in two iron tanks joined by pipes. One tank was forward of the midships engine room and the other was aft. The ship also featured a set of 21 vertical watertight compartments for extra buoyancy. The ship had a length overall of 56 metres (184 ft), a beam of 8.2 metres (27 ft), and a draft of 2.7 metres (9 ft). Unlike later Nobel tankers, the Zoroaster design was built small enough to sail from Sweden to the Caspian by way of the Baltic Sea, Lake Ladoga, Lake Onega, the Rybinsk and Mariinsk Canals and the Volga River. The aft and the stern was put together and then dismantled to make room for the mid-section as the Caspian Sea was reached.
In 1883, oil tanker design took a large step forward. Working for the Nobel company, British engineer Colonel Henry F. Swan designed a set of three Nobel tankers. Instead of one or two large holds, Swan's design used several holds which spanned the width, or beam, of the ship. These holds were further subdivided into port and starboard sections by a longitudinal bulkhead. Earlier designs suffered from stability problems caused by the free surface effect, where oil sloshing from side to side could cause a ship to capsize. But this approach of dividing the ship's storage space into smaller tanks virtually eliminated free-surface problems. This approach, almost universal today, was first used by Swan in the Nobel tankers Blesk, Lumen, and Lux.
Others point to Glückauf, another design of Colonel Swan, as being the first modern oil tanker. It adopted the best practices from previous oil tanker designs to create the prototype for all subsequent vessels of the type. It was the first dedicated steam-driven ocean-going tanker in the world and was the first ship in which oil could be pumped directly into the vessel hull instead of being loaded in barrels or drums. It was also the first tanker with a horizontal bulkhead; its features included cargo valves operable from the deck, cargo main piping, a vapor line, cofferdams for added safety, and the ability to fill a ballast tank with seawater when empty of cargo. The ship was built in Britain, and was purchased by Wilhelm Anton Riedemann, an agent for the Standard Oil Company along with several of her sister ships. After Glückauf was lost in 1893 after being grounded in fog, Standard Oil purchased the sister ships.
The 1880s also saw the beginnings of the Asian oil trade. The idea that led to moving Russian oil to the Far East via the Suez Canal was the brainchild of two men: importer Marcus Samuel and shipowner/broker Fred Lane. Prior bids to move oil through the canal had been rejected by the Suez Canal Company as being too risky. Samuel approached the problem a different way: asking the company for the specifications of a tanker it would allow through the canal.
Armed with the canal company's specifications, Samuel ordered three tankers from William Gray & Company in northern England. Named Murex, Conch and Clam, each had a capacity of 5,010 long tons of deadweight. These three ships were the first tankers of the Tank Syndicate, forerunner of today's Royal Dutch Shell company.
With facilities prepared in Jakarta, Singapore, Bangkok, Saigon, Hong Kong, Shanghai, and Kobe, the fledgling Shell company was ready to become Standard Oil's first challenger in the Asian market. On August 24, 1892, Murex became the first tanker to pass through the Suez Canal. By the time Shell merged with Royal Dutch Petroleum in 1907, the company had 34 steam-driven oil tankers, compared to Standard Oil's four case-oil steamers and 16 sailing tankers.