Oil Spills Caused by Marine Transportation

There are different methods of transportation of petroleum fluids. The main factor in selecting an appropriate transportation mode is the cost: the commodity is moved from one location to another at minimum cost. The cost of transportation is mainly a function of distance, volume of fluid, and type of fluid. In summary the best method of transportation of petroleum fluids at sea is by ship and on land by pipeline. However, offshore pipelines or submarine pipelines are commonly used for short distances and especially for gas transportation. In this section we discuss the principles of these methods of transportation and their role in oil spill occurrence.

Oil and Gas Transportation by Tankers

Marine (or maritime) transportation is a very old and a major method of transferring goods from one location to another through waterways, rivers, seas, oceans, lakes, dams, ports, channels, canals, chokepoints, and locks. Oil is the largest commodity moved by water, which is the most cost-effective and efficient method of transportation. In the US in 2012 almost 42% of all waterborne trade was comprised of crude oil or petroleum products. Just one average-size tanker of about 30,000 tons can carry as much oil product (gasoline, diesel, and heating oil) as 1,700 tanker trucks (API. 2020).

Papavinasam reported that in 2014 more than 9,300 tankers (about 11% of total world ships) were carrying oil across the world. According to EIA, the capacity of oil tankers increased from 2,000 million barrels in the year 2000 to 4,200 million barrels in 2019. However, if condensates and petroleum products are also included, the total petroleum maritime trade is more than 60 million b/d (EIA, 2019a). An oil tanker in the waters of New York Harbor is shown in Figure 3.18b.

The size of an oil tanker is based on the amount of oil that it can carry in metric tons, and this is known as dead weight (DWT) and varies from a few to several hundred thousand DWT as shown in Figure 3.19 (EIA, 2014). The largest normal tankers are very large crude carriers (VLCC) which can carry approximately 2 million barrels of oil. The relation between the volume of oil in barrels and its weight in metric tons depends on oil density or API gravity. For a typical oil with API gravity of 33 (specific gravity of 0.86) each ton of crude is equivalent to 7.31 barrels, while for heavier oils with API gravity of 27 (specific gravity of 0.892) the conversion factor from ton to barrel is about 7 (1 ton ~ 7 bbl).

An overview of tanker size, type, length and beam (maximum width), and draft is given in Table 3.2. A typical VLCC is about 300-330 m long with a beam of 50-60 m that may be loaded or discharged within a day with 2 million barrels of oil capacity. One of the major maritime trade routes for petroleum transportation is the Strait of Hormuz and the Persian Gulf region as shown in Figure 3.20. The volume of oil transported through this route is given in Table 3.3 (EIA, 2019a). As shown in this table, about one-third of total maritime petroleum trade in the world is through the Persian Gulf. Figure 3.21 shows the amount of maritime trade for both crude oil and its products through the Strait of Hormuz.

As about 60% of world oil production moves on marine routes, for the sake of global energy security there are security chokepoints for the routes specified. Chokepoints are narrow channels along global sea routes. Some of these channels are so narrow

Various tanker sizes and their uses in oil transportation (EIA, 2014)

FIGURE 3.19 Various tanker sizes and their uses in oil transportation (EIA, 2014).


Overview of Tanker Size and Type








205 m

29 m

16 m

Less than 50,000 dwt, mainly used for the transportation of refined products (gasoline, gasoil).


245 m

34 m

20 m

Approximately 80,000 dwt (average freight rate assessment).


285 m

45 m

23 m

Between 125.000 and 180.000 dwt. originally the maximum capacity of the Suez Canal.


330 m

55 m

28 m

Very large crude carrier. Up to around 320,000 dwt. Some can be accommodated by the expanded dimensions of the Suez Canal. The most common length is in the range of 300 to 330 meters.


415 m

63 m

35 m

Ultra large crude carrier. Capacity exceeding 320,000 dwt. The largest tankers ever built have a deadweight of over 550,000 dwt.

Source: ASTM MNL73.

Persian Gulf and Strait of Hormuz (EIA, 2019a)

FIGURE 3.20 Persian Gulf and Strait of Hormuz (EIA, 2019a).


Maritime Oil Trade in the Strait of Hormuz and the World






Total oil flows through the Strait of Hormuz






Crude and condensate






Petroleum products






World maritime oil trade






World total petroleum and other liquids consumption






LNG flows through the Strait of Hormuz (Tcf per year)






Source: EIA (2019).

that there are restrictions for the vessel going through them. The blockage of these chokepoints can lead to serious energy security issues in the world. Oil tankers going through chokepoints are vulnerable to pirates, terrorist attacks, political unrest, and hostilities as well as shipping accidents. Based on the volume of oil moved, the Strait of Hormuz (out of Persian Gulf) and the Strait of Malacca, linking the Indian and Pacific Oceans, are the world's most strategic chokepoints. Other major chokepoints are the Suez Canal (Mediterranean and Red Sea), the Strait of Bosporus (between the Mediterranean and Marmara Seas), the Danish Strait, and the Panama Canal linking the Atlantic and Pacific Oceans via the Sea of Caribbean. The volumes of

Flow of crude oil and petroleum products through the Strait of Hormuz in the Persian Gulf

FIGURE 3.21 Flow of crude oil and petroleum products through the Strait of Hormuz in the Persian Gulf.

oil moved through these chokepoints between 2007 and 2010 are given in Table 3.4 (ASTM MNL73). The Suez Canal connects the Red Sea and Mediterranean Sea and is a critical chokepoint because of the large volume of crude oil and LNG moved from the Persian Gulf to Europe and North America. The SUMED pipeline accounts for about 8% of global LNG trade (EIA. 2019a).

One of the worst oil spill accidents known as the SS Atlantic Empress was caused by the collision of two oil tankers about 10 miles off the coast of Tobago in the Caribbean. A Greek oil tanker SS Atlantic Empress collided with Aegean Captain

oil tanker during a tropical rainstorm on July 19, 1979. Following the collision, both


Volume of Crude Oil and Petroleum Products Transported through World Chokepoints, 2007-2010











Turkish Straits





Danish Straits





Strait of Hormuz





Panama Canal





Suez Canal and Sumed Pipeline





Sources: EIA and ASTM MNL73.

vessels began spilling about 287,000 tons (more than 2 million barrels) of crude oil, causing fire on the ship and killing several crewmen (ITOPF, 2020).

Another accident occurred on 15 November, 1979, when a Romanian tanker Independenta collided with the Greek cargo Evriali at the entrance of the Bosphorous in Turkey. About 94,000 tons of Libyan oil spilled and caught fire, causing the deaths of some 42 crew members. Further explosions occurred in December causing a greater release of oil (ITOPF, 2020). A more recent example although at a smaller size occurred on February 22, 2014, when a barge collided with a towboat which caused the leak of 750 barrels of crude oil into the Mississippi River in the United States (NOAA, 2019). An oil tanker carrying 270,000 metric tons of crude oil from Kuwait to India caught fire on September 3, 2020 as a result of a boiler explosion in the engine room. The ship was the Panama-registered MT New Diamond, and the accident occurred off the coast of Sri Lanka, and it was confirmed that a sailor was killed although the fire was brought under control and the ship was towed with the help of the Indian Navy (https://www.thehindu.com/news/international, September 5, 2020).

When two tankers or two vessels collide with each other, the term collision is used. However, when a ship or tanker strikes a stationary object it is also referred to as an allision, although these two terms sometimes are used instead of each other. An example of an allision is the Exxon Valdez accident (Figure 3.22). The Exxon Valdez oil spill was one of the largest oil spills in the US, and occurred when the oil tanker ran hard aground on Bligh Reef on March 24, 1989, spilling 11 million gallons of crude oil (about 37,000 tons or 270,000 barrels), and was the largest oil

The Exxon Valdez oil spill was caused when a tanker ran hard aground (NOAA photo)

FIGURE 3.22 The Exxon Valdez oil spill was caused when a tanker ran hard aground (NOAA photo).

spill disaster in American history at that time. A storm blew in, causing oil to spread widely and polluting some 1,000 miles of coastline and killing hundreds of thousands of birds and animals (Leahy, 2019).

At the height of the BP oil spill crisis on May 25, 2010, Malaysian-registered tanker Bunga Kelana 3 was damaged in a collision with another ship, spilling 2,000 tons of light crude oil in the Strait of Singapore, one of the most important shipping lanes in the w'orld. The speed of response reduced the impact on the environment as was reported by Reuters (ABC, May 25, 2010). Perhaps the worst oil tanker collision occurred on January 6, 2018, when two tankers collided off the coast of China about 300 km from Shanghai. An Iranian oil tanker, the Sanchi, lost 117,000 tons or nearly 1 million barrels of condensate, assuming specific gravity of 0.75. The gas condensate was highly toxic and the vessel caught fire, killing all 32 crew members and sinking after a week (Leahy, 2019). More details about these oil spills are given in Chapter 4.

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