Editing Oil spill (section)

==Sources and rate of occurrence==
Oil spills can be caused by human error, natural disasters, technical failures or deliberate releases.<ref>{{Cite journal|date=June 2010|title=Background on Oil Spills. Cause and Response|journal=Congressional Digest|volume=89|issue=6|pages=165–166|issn=0010-5899}}</ref><ref>{{Cite web|date=February 5, 2019|title=How do oil spills happen?|url=https://response.restoration.noaa.gov/training-and-education/education-students-and-teachers/how-do-spills-happen.html|access-date=2021-05-27|website=Office of Response and Restoration}}</ref> It is estimated that 30–50% of all oil spills are directly or indirectly caused by human error, with approximately 20–40% of oil spills being attributed to equipment failure or malfunction.<ref name=":0">{{Cite book|last1=Michel|first1=Jacqueline|title=Fossil Fuels|last2=Fingas|first2=Merv|publisher=Marcus Enterprise LLC, USA & University of South Carolina, USA|year=2016|isbn=978-981-4699-99-0|editor-last=Crawley|editor-first=Gerard M|url=https://doi.org/10.1142/9789814699983_0007|pages=160|chapter=Chapter 7: Oil spills: Causes, Consequences, Prevention and Countermeasures|doi=10.1142/9789814699983_0007}}</ref> Causes of oil spills are further distinguished between deliberate releases, such as operational discharges or acts of war and accidental releases. Accidental oil spills are in the focus of the literature, although some of the largest oil spills ever recorded, the [[Gulf War oil spill|Gulf War Oil Spill]] (sea based) and [[Kuwaiti Oil Fires]] (land based) were deliberate acts of war.<ref name=":1">{{Cite journal|last=Jernelöv|first=Arne|date=2010|title=The Threats from Oil Spills: Now, Then and in the Future|journal=Ambio|volume=39|issue=5–6|pages=353–366|doi=10.1007/s13280-010-0085-5|pmid=21053719|pmc=3357709|bibcode=2010Ambio..39..353J }}</ref> The academic study of sources and causes of oil spills identifies vulnerable points in oil transportation infrastructure and calculates the likelihood of oil spills happening. This can then guide prevention efforts and regulation policies<ref>{{Cite journal|last1=Bertolini|first1=Massimo|last2=Bevilacqua|first2=Maurizio|date=2006|title=Oil pipeline spill cause analysis A classification tree approach|journal=Journal of Quality in Maintenance Engineering|volume=12|issue=2|pages=186–198|doi=10.1108/13552510610667192}}</ref>

=== Natural seeps ===
Around 40–50% of all oil released into the oceans stems from natural seeps from seafloor rocks. This corresponds to approximately 600,000 tons annually on a global level. While natural seeps are the single largest source of oil spills, they are considered less problematic because ecosystems have adapted to such regular releases. For instance, on sites of natural oil seeps, ocean bacteria have evolved to digest oil molecules.<ref name=":2">{{Cite web|last1=Dell'Amore|first1=Christine|last2=Nunez|first2=Christina|date=March 25, 2014|title=3 Surprising Sources of Oil Pollution in the Ocean|url=https://www.nationalgeographic.com/science/article/140325-texas-pollution-oil-spills-animals-science|access-date=2021-05-27|website=National Geographic}}</ref><ref name=":3">{{Cite journal|last=Burgherr|first=Peter|date=2007|title=In-depth analysis of accidental oil spills from tankers in the context of global spill trends from all sources|url=|journal=Journal of Hazardous Materials|volume=140|issue=1–2|pages=245–256|doi=10.1016/j.jhazmat.2006.07.030|pmid=16942835|bibcode=2007JHzM..140..245B }}</ref><ref name=":1" />

=== Oil tankers and vessels ===
Vessels can be the source of oil spills either through operational releases of oil or in the case of [[oil tanker]] accidents. As of 2007, operational discharges from vessels were estimated to account for 21% of oil releases from vessels.<ref name=":3" /> They occur as a consequence of failure to comply with regulations or arbitrary discharges of waste oil and water containing such oil residues.<ref name=":4">{{Cite book|last1=Mu|first1=Lin|title=Information Engineering of Emergency Treatment for Marine Oil Spill Accidents|last2=Wang|first2=Lizhe|last3=Yan|first3=Jining|publisher=CRC Press|year=2019|isbn=9780429289101|location=Taylor & Francis Group|pages=1–30|chapter=Emergency Response System for Marine Oil Spill Accidents}}</ref> Such operational discharges are regulated through the [[MARPOL 73/78|MARPOL convention]].<ref>{{Cite web|title=MARPOL Annex I – Prevention of Pollution by Oil|url=https://www.imo.org/en/OurWork/Environment/Pages/OilPollution-Default.aspx|access-date=2021-05-27|website=International Maritime Organization}}</ref> Operational releases are frequent, but small in the amount of oil spilled per release, and are often not in the focus of attention regarding oil spills.<ref name=":3" /> There has been a steady decrease of operational discharges of oil, with an additional decrease of around 50% since the 1990s.<ref name=":1" />

{{as of|2007|post=,}} accidental oil tank vessel spills accounted for approximately 8–13% of all oil spilled into the oceans.<ref name=":3" /><ref name=":5">{{Cite journal|last1=Galieriková|first1=Andrea|last2=Materna|first2=Matúš|date=2020|title=World Seaborne Trade with Oil: One of Main Cause for Oil Spills?|journal=Transportation Research Procedia|volume=44|pages=297–304|doi=10.1016/j.trpro.2020.02.039|s2cid=216537436|doi-access=free}}</ref> The main causes of oil tank vessel spills were collision (29%), grounding (22%), mishandling (14%) and sinking (12%), among others.<ref name=":3" /><ref>{{Cite journal|last=Yamada|first=Yasuhira|date=October 2009|title=The Cost of Oil Spills from Tankers in Relation to Weight of Spilled Oil|journal=Marine Technology|volume=46|issue=4|pages=219–228|doi=10.5957/mtsn.2009.46.4.219}}</ref> Oil tanker spills are considered a major ecological threat due to the large amount of oil spilled per accident and the fact that major sea traffic routes are close to [[Large marine ecosystem|Large Marine Ecosystems]].<ref name=":3" /> Around 90% of the world's oil transportation is through oil tankers, and the absolute amount of seaborne oil trade is steadily increasing.<ref name=":5" /> However, there has been a reduction of the number of spills from oil tankers and of the amount of oil released per oil tanker spill.<ref name=":5" /><ref name=":1" /> In 1992, [[MARPOL 73/78|MARPOL]] was amended and made it mandatory for large tankers (5,000 dwt and more) to be fitted with [[double hull]]s.<ref>{{Cite web|title=Construction Requirements for Oil Tankers – Double Hulls|url=https://www.imo.org/en/OurWork/Environment/Pages/constructionrequirements.aspx|access-date=2021-05-27|website=International Maritime Organization}}</ref> This is considered to be a major reason for the reduction of oil tanker spills, alongside other innovations such as [[Global Positioning System|GPS]], sectioning of vessels and [[sea lane]]s in narrow straits.<ref name=":1" /><ref name=":3" />

In 2023, the International Tanker Owners Pollution Federation (ITOPF) documented a significant oil spill incident of over 700 tonnes and nine medium spills ranging between 7 and 700 tonnes. The major spill occurred in Asia involving heavy fuel oil, and the medium spills were scattered across Asia, Africa, Europe, and America, involving various oil types.<ref name=":10">{{Cite web |title=Oil Tanker Spill Statistics 2023 – ITOPF |url=https://www.itopf.org/knowledge-resources/data-statistics/statistics/ |access-date=2024-04-12 |website=itopf.org}}</ref>

The total volume of oil released from these spills in 2023 was approximately 2,000 tonnes. This contributes to a trend of decreased oil spill volumes and frequencies over the decades. Comparatively, the 1970s averaged 79 significant spills per year, which drastically reduced to an average of about 6.3 per year in the 2010s, and has maintained a similar level in the current decade.<ref name=":10" />

The reduction in oil spill volume has also been substantial over the years. For instance, the 1990s recorded 1,134,000 tonnes lost, mainly from 10 major spills. This figure decreased to 196,000 tonnes in the 2000s and 164,000 tonnes in the 2010s. In the early 2020s, approximately 28,000 tonnes have been lost, predominantly from major incidents.<ref name=":10" />

=== Offshore oil platforms ===
[[File:Figure 1 Use of Chemical Dispersants during a Subsurface Oil Spill (51787831851).jpg|thumb|upright=1.3|Chemical dispersants may be deployed from boats, planes, and underwater vehicles in response to an offshore oil spill]]
Accidental spills from [[oil platform]]s nowadays account for approximately 3% of oil spills in the oceans.<ref name=":3" /> Prominent offshore oil platform spills typically occurred as a result of a [[Blowout (well drilling)|blowout]]. They can go on for months until relief wells have been drilled, resulting in enormous amounts of oil leaked.<ref name=":1" /> Notable examples of such oil spills are [[Deepwater Horizon oil spill|Deepwater Horizon]] and [[Ixtoc I oil spill|Ixtoc I]]. While technologies for drilling in deep water have significantly improved in the past 30–40 years, oil companies move to drilling sites in more and more difficult places. This ambiguous development results in no clear trend regarding the frequency of offshore oil platform spills.<ref name=":1" />

=== Pipelines ===
As of 2010, overall, there has been a substantial increase of pipeline oil spills in the past four decades.<ref name=":1" /> Prominent examples include [[Environmental issues in the Niger Delta|oil spills of pipelines in the Niger Delta]]. Pipeline oil spills can be caused by trawling of fishing boats, natural disasters, pipe corrosion, construction defects, sabotage, or an attack,<ref name=":4" /> as with the [[Caño Limón–Coveñas pipeline|Caño Limón-Coveñas pipeline]] in Colombia.

[[Pipeline transport|Pipelines]] as sources of oil spills are estimated to contribute 1% of oil pollution to the oceans.<ref name=":3" /> Reasons for this are underreporting, and many oil pipeline leaks occur on land with only fractions of that oil reaching the oceans.

=== Other sources ===
[[Recreational boat]]s can spill oil into the ocean because of operational or human error and unpreparedness. The amounts are however small, and such oil spills are hard to track due to underreporting.<ref name=":2" />

Oil can reach the oceans as oil and fuel from land-based sources.<ref name=":0" /> It is estimated that runoff oil and oil from rivers are responsible for 11% of oil pollution to the oceans.<ref name=":3" /> Such pollution can also be oil on roads from land vehicles, which is then flushed into the oceans during rainstorms.<ref name=":2" /> Purely land-based oil spills are different from maritime oil spills in that oil on land does not spread as quickly as in water, and effects thus remain local.<ref name=":0" />