Background
ITOPF maintains a database of oil spills from tankers, combined carriers and barges. This contains information on ACCIDENTAL spillages since 1970, except those resulting from acts of war.
The data held includes the type of oil spilt, the spill amount, the cause and location of the incident and the vessel involved. For historical reasons, spills are generally categorised by size:<7 tonnes, 7-700 tonnes and >700 tonnes (<50 bbls, 50-5,000 bbls, >5,000 bbls), although the actual amount spilt is also recorded. Information is now held on nearly 10,000 incidents, the vast majority of which (81%) fall into the smallest category i.e. <7 tonnes.
Information is gathered from both published sources, such as the shipping press and other specialist publications, and also from vessel owners and their insurers. Unsurprisingly, information from published sources generally relates to large spills, often resulting from collisions, groundings, structural damage, fires and explosions, whereas the majority of individual reports relate to small operational spillages. Complete reporting of this latter type of spill is clearly difficult to achieve.
It should be noted that the figures for the amount of oil spilt in an incident include all oil lost to the environment, including that which burnt or remained in a sunken vessel. There is considerable annual variation in both the incidence of oil spills and the amounts of oil lost. Whilst we strive to maintain precise records for all spill information, we cannot guarantee the information taken from shipping press and other sources is complete or accurate. Consequently, the figures in the following tables, and any averages derived from them should be viewed with an element of caution.
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Numbers and Amounts Spilt
Number of Oil Spills
The incidence of large spills is relatively low and detailed statistical analysis is rarely possible, consequently emphasis is placed on identifying trends. Thus, it is apparent from Table 1 that the number of large spills (>700 tonnes) has decreased significantly during the last 42 years during which records have been kept. The average number of major spills for the previous decade (2000-2009) is just over three, approximately eight times less than for the 1970s. Looking at this downward trend from another perspective, 55% of the large spills recorded occurred in the 1970s, and this percentage has decreased each decade to 7% in the 2000s (Figure 1).
A decline can also be observed with medium sized spills (7-700 tonnes) in Table 1. Here, the average number of spills in the 2000s was close to 15, whereas in the 1990s the average number of spills was almost double this number.
For 2011, one large spill was recorded (Figure 2 and Table 1). Four medium spills were also recorded in 2011, representing the lowest annual figure recorded for the second year in a row for this category. The total of all spills over 7 tonnes for 2011 is the lowest so far and is a significant reduction compared to the average for the previous decade.
Figure 1: Major spills as a percentage of those recorded from 1970 to 2009 per decade
Figure 2: Number of large spills (over 700 tonnes) from 1970 to 2011
Figure 3: Number of medium sized (7-700 tonnes) and large (>700 tonnes) spills per decade from 1970-2011
Quantities of Oil Spilt
The vast majority of spills are small (i.e. less than 7 tonnes) and data on numbers and amounts is incomplete due to the inconsistent reporting of smaller incidents worldwide.
Reports on spills of 7 tonnes and above tend to be more reliable and information from these is included in the database to give a series of annual estimates of the total quantity spilt for the years 1970-2011. These amounts are rounded to the nearest thousand where practical.
Approximately 5.7 million tonnes of oil were lost as a result of tanker incidents from 1970 to 2011. However, as Figure 4 and 6 indicate, the volume of oil spilt from tankers demonstrates a significant improvement through the decades. Consistent with the reduction in the number of oil spills from tankers, the volume of oil spilt also shows a marked reduction. For instance, from Table 2 it is interesting to observe that an amount greater than the total quantity of oil spilt in the decade 2000 to 2009 (211,000 tonnes) was spilt in several single years in earlier decades.
The total amount of oil lost to the environment in 2011 is the lowest on record so far (Table 2 and Figure 4).
Figure 4: Quantities of oil spilt over 7 tonnes, 1970 to 2011
Figure 5: Spills over 7 tonnes per decade showing the influence of a relatively small number of comparatively large spills on the overall figure
As demonstrated in Figure 5, when looking at the frequency and quantities of oil spilt, it should be noted that a few very large spills are responsible for a high percentage of oil spilt. For example, in more recent decades the following can be seen:
• In the 1990s there were 361 spills over 7 tonnes, resulting in 1,137,000 tonnes of oil lost; 73% of this amount was spilt in just 10 incidents.
• In the 2000s there were 181 spills over 7 tonnes, resulting in 210,000 tonnes of oil lost; 44% of this amount was spilt in just 2 incidents.
The figures for a particular year may therefore be severely distorted by a single large incident. This is clearly illustrated by incidents such as ATLANTIC EMPRESS (1979), 287,000 tonnes spilt; CASTILLO DE BELLVER (1983), 252,000 tonnes spilt and ABT SUMMER (1991), 260,000 tonnes spilt.
Figure 6: Oil spilt per decade from 1970 to 2009 (excluding 2010-2011) as a percentage of the total spilt
Major Oil Spills
Table 3 below gives a brief summary of 20 major oil spills since 1967. The map in Figure 7 shows where they occurred. A number of these incidents, despite their large size, caused little or no environmental damage as the oil was spilt some distance offshore and did not impact coastlines. It is for this reason that some of the names listed may be unfamiliar. EXXON VALDEZ is included for comparison although this incident falls some way outside the group.
| Position | Shipname | Year | Location | Spill Size (tonnes) |
|---|---|---|---|---|
| 1 | Atlantic Empress | 1979 | Off Tobago, West Indies | 287,000 |
| 2 | ABT Summer | 1991 | 700 nautical miles off Angola | 260,000 |
| 3 | Castillo de Bellver | 1983 | Off Saldanha Bay, South Africa | 252,000 |
| 4 | Amoco Cadiz | 1978 | Off Brittany, France | 223,000 |
| 5 | Haven | 1991 | Genoa, Italy | 144,000 |
| 6 | Odyssey | 1988 | 700 nautical miles off Nova Scotia, Canada | 132,000 |
| 7 | Torrey Canyon | 1967 | Scilly Isles, UK | 119,000 |
| 8 | Sea Star | 1972 | Gulf of Oman | 115,000 |
| 9 | Irenes Serenade | 1980 | Navarino Bay, Greece | 100,000 |
| 10 | Urquiola | 1976 | La Coruna, Spain | 100,000 |
| 11 | Hawaiian Patriot | 1977 | 300 nautical miles off Honolulu | 95,000 |
| 12 | Independenta | 1979 | Bosphorus, Turkey | 95,000 |
| 13 | Jakob Maersk | 1975 | Oporto, Portugal | 88,000 |
| 14 | Braer | 1993 | Shetland Islands, UK | 85,000 |
| 15 | Khark 5 | 1989 | 120 nautical miles off Atlantic coast of Morocco | 80,000 |
| 16 | Aegean Sea | 1992 | La Coruna, Spain | 74,000 |
| 17 | Sea Empress | 1996 | Milford Haven, UK | 72,000 |
| 18 | Nova | 1985 | Off Kharg Island, Gulf of Iran | 70,000 |
| 19 | Katina P | 1992 | Off Maputo, Mozambique | 66,700 |
| 20 | Prestige | 2002 | Off Galicia, Spain | 63,000 |
| 35 | Exxon Valdez | 1989 | Prince William Sound, Alaska, USA | 37,000 |
Table 3: Major oil spills Since 1967
Figure 7: Location of major spills (click map to view larger version in PDF format)
Seaborne Oil Trade
Apart from a fall in the early 1980s during the worldwide economic recession, seaborne oil trade has grown steadily from 1970 (Figure 8). While increased movements might imply increased risk, it is encouraging to observe however that downward trends in oil spills continue despite an overall increase in oil trading over the period.
Figure 8: Seaborne oil trade and number of tanker spills over 7 tonnes, 1970-2011
(crude and oil product*)
*Product vessels of 60,000 DWT and above
Causes of Spills
The causes and circumstances of oil spills are varied, but can have a significant effect on the final quantity spilt. The following analysis explores the incidence of spills of different sizes in terms of the operation that the vessel was undertaking at the time of the incident and the primary cause of the spill. For small and medium sized spills operations have been grouped into Loading/Discharging, Bunkering, Other Operations and Unknown Operations. Other Operations includes activities such as ballasting, de-ballasting, tank cleaning and when the vessel is en route.
Reporting of larger spills tends to provide much more information and accuracy, which has allowed further breakdown of vessel operations. Therefore, operations for larger spills have been grouped into Loading/Discharging, Bunkering, At Anchor (Inland/Restricted waters), At Anchor (Open water), Underway (Open water), Underway (Inland/Restricted waters), Other Operations and Unknown Operations. The primary causes have been designated to Allisions/Collisions, Groundings, Hull Failures, Equipment Failures, Fire and Explosion, and Other/Unknown. Other causes include events such as heavy weather damage and human error. Spills where the relevant information is not available have been designated as Unknown.
Small and medium sized spills account for 95% of all the incidents recorded; a large percentage of these spills, 40% and 29% respectively, occurred during loading and discharging operations which normally take place in ports and oil terminals (Figures 9 and 12). While the cause of these spills is largely unknown it can be seen that equipment and hull failures account for approximately 46% of these incidents for both size categories (Figures 11 and 14) . Nevertheless, there is a significant difference in the percentage of allisions, collisions and groundings between these two size groups where we see the percentage increasing from 2% for smaller spills to 35% for medium spills (Figure 14).
Large spills account for the remaining 5% of all the incidents recorded and the occurrence of these incidents has significantly decreased over the past 42 years. From Figure 15, it can be seen that 50% of large spills occurred while the vessels were underway in open water; allisions, collisions and groundings accounted for 58% of the causes for these spills (Figure 17). These same causes account for an even higher percentage of incidents when the vessel was underway in inland or restricted waters, being linked to some 95% of spills.
Perhaps unsurprisingly activities during loading or discharging result in significantly more small or medium sized spills than large spills. However, large spills do still occur during loading and discharging, and from Figure 17 and Table 6, it can be seen that 61% of these incidents are caused by fires, explosions and equipment failures.
Figure 9: Incidence of spills <7 tonnes by operation at time of incident, 1974-2011
Figure 10: Incidence of spills <7 tonnes by cause, 1974-2011
Figure 11: Incidence of spills <7 tonnes by operation at time of incident and primary cause of spill, 1974-2011
| Operations | ||||
|---|---|---|---|---|
Loading/ Discharging |
Bunkering | Other Operations | Unknown | |
3156 |
563 |
1270 |
2852 |
|
Causes |
||||
Collisions |
1 |
2 |
11 |
168 |
Groundings |
2 |
0 |
9 |
228 |
Hull failures |
324 |
10 |
47 |
196 |
Equipment failures |
1123 |
104 |
250 |
202 |
Fires/Explosions |
50 |
5 |
34 |
84 |
Other/Unknown |
1656 |
442 |
919 |
1974 |
Total |
3156 |
563 |
1270 |
2852 |
Table 4: Incidence of spills <7 tonnes by operation at time of incident and primary cause of spill, 1974-2011
Figure 12: Incidence of spills 7-700 tonnes by operation at time of incident, 1970-2011
Figure 13: Incidence of spills 7-700 tonnes by cause, 1970-2011
Figure 14: Incidence of spills 7-700 tonnes by operation at time of incident and primary cause of spill, 1970-2011
| Operations | ||||
|---|---|---|---|---|
Loading/ Discharging |
Bunkering | Other Operations | Unknown | |
388 |
33 |
136 |
785 |
|
Causes |
||||
Collisions |
4 |
0 |
32 |
308 |
Groundings |
0 |
0 |
16 |
253 |
Hull failures |
36 |
4 |
10 |
50 |
Equipment failures |
141 |
6 |
17 |
38 |
Fires/Explosions |
8 |
0 |
13 |
26 |
Other/Unknown |
199 |
23 |
48 |
110 |
Total |
388 |
33 |
136 |
785 |
Table 5: Incidence of spills 7-700 tonnes by operation at time of incident and primary cause of spill, 1970-2011
Figure 15: Incidence of spills >700 tonnes by operation at time of incident, 1970-2011
Figure 16: Incidence of spills >700 tonnes by cause, 1970-2011
Figure 17: Incidence of spills >700 tonnes by operation at time of incident and primary cause of spill, 1970-2011. (One bunkering incident occurred in this size category but has not been included in the graph)
| Operations | ||||
|---|---|---|---|---|
| At anchor (Inland/Restricted) | At anchor (Open Water) |
Underway (Inland/Restricted) |
Underway (Open Water) |
|
13 |
9 |
82 |
225 |
|
Causes |
||||
Allisions/ Collisions |
6 |
5 |
33 |
65 |
Groundings |
4 |
2 |
45 |
66 |
Hull failures |
0 |
1 |
0 |
50 |
Equipment failures |
0 |
0 |
0 |
7 |
Fires/Explosions |
1 |
1 |
3 |
25 |
Other/Unknown |
2 |
0 |
1 |
12 |
Total |
13 |
9 |
82 |
225 |
| Operations cont... | |||
|---|---|---|---|
Loading/ discharging |
Bunkering | Other operations/unknown | |
41 |
1 |
83 |
|
Causes |
|||
Allisions/ Collisions |
1 |
0 |
24 |
Groundings |
2 |
0 |
29 |
Hull failures |
0 |
0 |
8 |
Equipment failures |
11 |
0 |
1 |
Fires/Explosions |
14 |
1 |
9 |
Other/Unknown |
13 |
0 |
12 |
Total |
41 |
1 |
83 |
Table 6: Incidence of spills >700 tonnes by operation at time of incident and primary cause of spill, 1970-2011
Further information is available in:
Trends in Oil Spills from Tanker Ships 1995-2004 (2005) [603kb]
by Keisha Huijer
Paper presented at the 28th Arctic and Marine Oilspill Program (AMOP) Technical Seminar, 7-9 June 2005, Calgary, Canada