NOAA's Response and Restoration Blog

An inside look at the science of cleaning up and fixing the mess of marine pollution


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How Much Oil Is on That Ship?

The massive container ship Benjamin Franklin pulls into the Port of Seattle.

The container ship Benjamin Franklin, the largest cargo ship to visit the United States, arrives in Elliott Bay at the Port of Seattle on February 29, 2016. Credit: Don Wilson/Port of Seattle

Like many people with an interest in the maritime industry, I’ve been following the story of the huge container ship Benjamin Franklin that recently visited Seattle’s port.

The news stories about it were full of superlatives. It was the largest cargo vessel to visit the United States, measuring 1,310 feet in length, or longer than the height of two Space Needles.

This massive ship can carry 18,000 shipping containers, known in the business as 20-foot equivalent units or TEUs. That is more than double the cargo of most container ships calling on the Port of Seattle. Loaded on a train (and most of them will be) those containers would stretch more than 68 miles, or the distance from Tacoma, Washington, to Everett.

Considering this ship’s massive size made me wonder how much fuel is on board. After some research, I found out: about 4.5 million gallons. That makes it just a bit bigger than my sailboat which holds only 20 gallons of fuel.

Understanding the potential volumes of oil (either as fuel or cargo) carried on ships is a major consideration in spill response planning.

All tank vessels (tankers and barges) and all non-tank vessels (freighters, cruise ships, etc.) larger than 400 gross tons have to have vessel response plans. Key metrics in those plans include listing the maximum amount of oil that could be spilled (known as the worst case discharge) and the maximum most probable discharge, which, for non-tank vessels, is generally defined as 10% of the vessel’s total fuel capacity.

What about other types of vessels? How much oil in the form of fuel or cargo do they typically carry?

Here are some approximate numbers, many of which are pulled from this Washington State Department of Ecology report [PDF]:

  • Small speedboat (12–20 feet): 6–20 gallons
  • Sailing yacht (33–45 feet) : 30–120 gallons
  • Motor yacht (40–60 feet) : 200–1,200 gallons
  • Large tanker truck: 5,000–10,000 gallons
  • Small tugboat (30–60 feet): 1,500–25,000 gallons
  • Petroleum rail car: 30,000 gallons
  • Boeing 747 airplane: 50,000–60,000 gallons
  • Ocean-going tugboat (90–150 feet): 90,000–190,000 gallons
  • Puget Sound jumbo ferry (440 feet): 130,000 gallons
  • Microsoft co-founder Paul Allen’s yacht M/V Octopus (416 feet): 224,000 gallons
  • Bulk carrier of commodities such as grain or coal (500–700 feet): 400,000–800,000 gallons
  • Large cruise ship (900–1,100 feet): 1–2 million gallons
  • Inland tank barge (200–300 feet): 400,000–1.2 million gallons
  • Panamax container ship that passes through the Panama Canal (960 feet): 1.5–2 million gallons
  • Container ship Benjamin Franklin (1,310 feet): 4.5 million gallons
  • Ocean-going tank barge (550–750 feet): 7 million–14 million gallons
  • T/V Exxon Valdez and similar large oil tankers (987 feet): 55 million gallons

Thanks to developing technologies, such “mega-vessels” as the Benjamin Franklin appear to be on the rise, a trend we’re watching along with the International Tanker Owners Pollution Federation and University of Washington.

How will these larger ships carrying more oil affect the risk of oil spills and how should NOAA prepare for these changes? Stay tuned.


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Alaska Updates Plan for Using Dispersants During Oil Spills

Humpback whale and seabirds at surface of Bering Sea with NOAA ship beyond.

By breaking crude oils into smaller droplets, chemical dispersants reduce the surface area of an oil slick as well as the threats to marine life at the ocean surface, such as whales and seabirds. (NOAA)

While the best way to deal with oil spills in the ocean is to prevent them in the first place, when they do happen, we need to be ready. Cleanup is difficult, and there are no magic remedies to remove all the oil. Most big oil spills require a combination of cleanup tools.

This week the Alaska Regional Response Team, an advisory council for oil spill responses in Alaska, has adopted a revised plan for one of the most controversial tools in the toolbox: Chemical dispersants.

How Dispersants Are Used in Oil Spills

Dispersants are chemical compounds which, when applied correctly under the right conditions, break crude oils into smaller droplets that mix down into the water column. This reduces not only the surface area of an oil slick but also the threats to marine life at the ocean surface. By making the oil droplets smaller, they become much more available to natural degradation by oil-eating microbes.

Dispersants are controversial for many reasons, notably because they don’t remove oil from the marine environment. Mechanical removal methods are always preferred, but we also know that during large oil spills, containment booms and skimmers can get overwhelmed and other pollution response tools may be necessary. This is a big concern especially in Alaska, where weather and remote locations increase the logistical challenges inherent in a large scale oil spill response.

Although dispersants get a lot of attention because of their extensive use after the 2010 Deepwater Horizon oil spill, they actually are used rarely during oil spills. In fact, dispersants have only been applied to about two dozen spills in the United States in the last 40 years. The only time they were tested during an actual spill in Alaska was during the Exxon Valdez oil spill in 1989.

Some oils like light and medium crude are often dispersible and others, like heavy fuel oils, often are not. In some cases dispersants have worked and in others they haven’t. The results of the Exxon Valdez testing were unclear and still subject to debate. So, why have a plan for something that is rarely used and may not be successful?

Probably the biggest reason is pragmatic. Dispersants work best on fresh, unweathered oil. Ideally, they should be applied to oil within hours or days of a spill. Because time is such a critical factor to their effectiveness, dispersants need to be stockpiled in key locations, along with the associated aircraft spraying and testing equipment. People properly trained to use that equipment need to be ready to go too.

A New Plan for Alaska

Airplane sprays dispersants over an oil slick in the Gulf of Mexico.

Although only used once in an Alaskan oil spill, dispersants have already been an approved oil spill response tool in the state for a number of years. This new plan improves the decision procedures and designates areas where dispersant use may be initiated rapidly. (U.S. Environmental Protection Agency)

Now, dispersants have already been an approved oil spill response tool in Alaska [PDF] for a number of years. This new plan improves the decision procedures and designates areas where dispersant use may be initiated rapidly while still requiring notification of the natural resource trustees, local and tribal governments, and other stakeholders before actual use.

Alaska’s new plan specifies all the requirements for applying dispersants on an oil spill in Alaskan waters and includes detailed checklists to ensure that if dispersants are used, they have a high probability of success.

The new plan sets up a limited preauthorization zone in central and western Alaska, and case-by-case procedures for dispersant use elsewhere in Alaska. The plan also recognizes that there are highly sensitive habitats where dispersant use should be avoided.

In addition, preauthorization for using dispersants exists only for oil spills that happen far offshore. Most states have similar preauthorization plans that allow dispersant use starting three nautical miles offshore. The new Alaska plan starts at 24 miles offshore.

We realize that even far offshore, there may be areas to avoid, which is why all of the spill response plans in central and western Alaska will be revised over the next two years. This will occur through a public process to identify sensitive habitats where dispersant use would be subject to additional restrictions.

Planning for the Worst, Hoping for the Best

As the NOAA representative to the Alaska Regional Response Team, I appreciate all of the effort that has gone into this plan. I am grateful we developed the many procedures through a long and inclusive planning process, rather than in a rush on a dark and stormy night on the way to an oil spill.

But I hope this plan will never be needed, because that will mean that a big oil spill has happened. Nobody wants that, especially in pristine Alaskan waters.

Any decision to use dispersants will need to be made cautiously, combining the best available science with the particular circumstances of an oil spill. In some cases, dispersants may not be the best option, but in other scenarios, there may be a net environmental benefit from using dispersants. Having the dispersants, equipment, plans, and training in place will allow us to be better prepared to make that critical decision should the time come.

At the same time, NOAA and our partners are continuing to research and better understand the potential harm and trades-offs of dispersant use following the Deepwater Horizon oil spill. We are participating in an ongoing effort to understand the state of the science on dispersants and their potential use in Arctic waters. (The University of New Hampshire is now accepting comments on the topic of dispersant efficacy and effectiveness.)

You can find Alaska’s new dispersant policy and additional information at the Alaska Regional Response Team website at www.alaskarrt.org.

For more information on our work on dispersants, read the April 2015 article, “What Have We Learned About Using Dispersants During the Next Big Oil Spill?” and July 2013 article, “Watching Chemical Dispersants at Work in an Oil Spill Research Facility.”


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Helping a 7-year-old Oceanographer Study Oil Spills in Washington’s Waters

A young boy drops wooden yellow cards off the side of a boat into water.

Dropping the first round of drift cards off a boat in Washington’s San Juan Islands, a kindergartner kicked off his experiment to study oil spills. (Used with permission of Alek)

One spring day in 2014, a shy young boy sidled up to the booth I was standing at during an open house hosted at NOAA’s Seattle campus. His blond head just peaking over the table, this then-six-year-old, Alek, accompanied by his mom and younger sister, proceeded to ask how NOAA’s oil spill trajectory model, GNOME, works.

This was definitely not the question I was expecting from a child his age.

After he set an overflowing binder onto the table, Alek showed me the printed-out web pages describing our oil spill model and said he wanted to learn how to run the model himself. He was apparently planning a science project that would involve releasing “drift cards,” small biodegradable pieces of wood marked with identifying information, into Washington’s Salish Sea to simulate where spilled oil might travel along this heavily trafficked route for oil tankers.

Luckily, Chris Barker, one of our oceanographers who run this scientific model, was nearby and I introduced them.

But that wasn’t my last interaction with this precocious, young oceanographer-in-training. Alek later asked me to serve on his science advisory committee (something I wish my middle school science fair projects had the benefit of having). I was in the company of representatives from the University of Washington, Washington State Department of Ecology, and local environmental and marine organizations.

Over the next year or so, I would direct his occasional questions about oil spills, oceanography, and modeling to the scientists in NOAA’s Office of Response and Restoration.

Demystifying the Science of Oil Spills

A hand-drawn map of oil tankers traveling from Alaska to Washington, a thank-you note on a post-it, and a hand-written card asking for donations.

Alek did a lot of work learning about how oil tankers travel from Alaska to Washington waters and about the threat of oil spills. He even fund-raised to cover the cost of materials for his drift cards. (NOAA)

According to the Washington Department of Ecology, the waters of the Salish Sea saw more than 7,000 journeys by oil tankers traveling to and from six oil refineries along its coast in 2013. Alek’s project was focused on Rosario Strait, a narrow eastern route around Washington’s San Juan Islands in the Salish Sea. There, he would release 400 biodegradable drift cards into the marine waters, at both incoming and outgoing tides, and then track their movements over the next four months.

The scientific questions he was asking in the course of his project—such as where spilled oil would travel and how it might affect the environment—mirror the types of questions our scientists and oil spill experts ask and try to answer when we advise the U.S. Coast Guard during oil spills along the coast.

As Alek learned, multiple factors influence the path spilled oil might take on the ocean, such as the oil type, weather (especially winds), tides, currents, and the temperature and salinity of the water. He attempted to take some of these factors into account as he made his predictions about where his drift cards would end up after he released them and how they would get there.

As with other drift card studies, Alek relied on people finding and reporting his drift cards when they turned up along the coast. Each drift card was stamped with information about the study and information about how to report it.

NOAA has performed several drift card studies in areas such as Hawaii, California, and Florida. One such study took place after the December 1976 grounding of the M/V Argo Merchant near Nantucket Island, Massachusetts, and we later had some of those drift cards found as far away as Ireland and France.

A Learning Experience

A young boy in a life jacket holding a yellow wooden card and sitting on the edge of a boat.

Alek released 400 biodegradable drift cards near Washington’s San Juan Islands in the Salish Sea, at both incoming and outgoing tides, and tracked their movements to simulate an oil spill. (Used with permission of Alek)

Of course, any scientist, young or old, comes across a number of challenges and questions in the pursuit of knowledge. For Alek, that ranged from fundraising for supplies and partnering with an organization with a boat to examining tide tables to decide when and where to release the drift cards and learning how to use Google Earth to map and measure the drift cards’ paths.

Only a couple weeks after releasing them, Alek began to see reports of his drift cards turning up in the San Juan Islands and even Vancouver Island, Canada, with kayakers finding quite a few of them.

As Alek started to analyze his data, we tried to help him avoid overestimating the area of water and length of coastline potentially affected by the simulated oil spill. Once released, oil tends to spread out on the water surface and would end up in patches on the shoreline as well.

Another issue our oceanographer Amy MacFadyen pointed out to Alek was that “over time the oil is removed from the surface of the ocean (some evaporates, some is mixed into the water column, etc.). So, the sites that it took a long time for the drift cards to reach would likely see less impacts as the oil would be much more spread out and there would be less of it.”

During his project, Alek was particularly interested in examining the potential impacts of an oil spill on his favorite marine organism, the Southern Resident killer whales (orcas) that live year-round in the Salish Sea but which are endangered. He used publicly available information about their movements to estimate where the killer whales might have intersected the simulated oil (the drift cards) across the Salish Sea.

Originally, Alek had hoped to estimate how many killer whales might have died as a result of a hypothetical oil spill in this area, but determining the impacts—both deadly and otherwise—of oil on marine mammals is a complicated matter. As a result, we advised him that there is too much uncertainty and not enough data for him to venture a guess. Instead, he settled on showing the number of killer whales that might be at risk of swimming through areas of simulated oil—and hence the killer whales that could be at risk of being affected by oil.

Ocean Scientist in Training

Google Earth view of the differing paths Alek's two drift card releases traveled around Washington's San Juan Islands and Canada's Vancouver Island.

A Google Earth view of the differing paths Alek’s two drift card releases traveled around Washington’s San Juan Islands and Canada’s Vancouver Island. Red represents the paths of drift cards released on an outgoing tide and yellow, the paths of cards released on an incoming tide. (Used with permission of Alek)

“I’d like to congratulate him on a successful drift card experiment,” said MacFadyen. “His results clearly show some of the features of the ocean circulation in this region.”

In a touching note in his final report, Alek dedicated his study to several great ocean scientists and explorers who came before him, namely, Sylvia Earle, Jacques Cousteau, William Beebe, and Rachel Carson. He was also enthusiastic in his appreciation of our help: “Thank you very very much for all of your help! I love what you do at NOAA. Maybe someday I will be a NOAA scientist!”

If you’re interested in learning more about Alek’s study and his results, you can visit his website www.oilspillscience.org, where you also can view a video summary of his project.


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Science of Oil Spills Training: Apply for Summer 2016

Group of Coast Guard members sit and stand at a table.

These trainings help new and mid-level spill responders increase their understanding of oil spill science when analyzing spills and making risk-based decisions. (NOAA)

NOAA‘s Office of Response and Restoration, a leader in providing scientific information in response to marine pollution, has scheduled a summer Science of Oil Spills (SOS) class in Seattle, Washington, June 6-10, 2016.

Currently, we are accepting applications for three SOS classes for these locations and dates:

  • Mobile, Alabama, the week of March 28, 2016
  • Ann Arbor, Michigan, the week of May 16, 2016
  • Seattle, Washington, the week of June 6, 2016

We will accept applications for these classes as follows:

  • For the Mobile class, the application period will be open until Friday, January 22. We will notify accepted participants by email no later than Friday, February 5.
  • For the Ann Arbor class, the application period will be open until Friday, March 11. We will notify accepted participants by email no later than Friday, March 25.
  • For the Seattle class, the application period will be open until Friday, April 1. We will notify accepted participants by email no later than Friday, April 15.

SOS classes help spill responders increase their understanding of oil spill science when analyzing spills and making risk-based decisions. They are designed for new and mid-level spill responders.

The trainings cover:

  • Fate and behavior of oil spilled in the environment.
  • An introduction to oil chemistry and toxicity.
  • A review of basic spill response options for open water and shorelines.
  • Spill case studies.
  • Principles of ecological risk assessment.
  • A field trip.
  • An introduction to damage assessment techniques.
  • Determining cleanup endpoints.

To view the topics for the next SOS class, download a sample agenda [PDF, 170 KB].

Please understand that classes are not filled on a first-come, first-served basis. We try to diversify the participant composition to ensure a variety of perspectives and experiences, to enrich the workshop for the benefit of all participants. Classes are generally limited to 40 participants.

For more information, and to learn how to apply for the class, visit the SOS Classes page.


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Science of Oil Spills Training Now Accepting Applications for Spring 2016

Two people closely examining rocks and seaweed on a shoreline.

These classes help prepare responders to understand the environmental risks and scientific considerations when addressing oil spills, and also include a field trip to a local beach to apply newly learned skills. (NOAA)

NOAA‘s Office of Response and Restoration, a leader in providing scientific information in response to marine pollution, has scheduled Science of Oil Spills (SOS) classes in two locations in spring 2016:

  • Mobile, Alabama the week of March 28, 2016
  • Ann Arbor, Michigan the week of May 16, 2016

We will accept applications for these classes as follows:

For the Mobile class, the application period will be open until Friday, January 22. We will notify accepted participants by email no later than Friday, February 5.

For the Ann Arbor class, the application period will be open until Friday, March 11. We will notify accepted participants by email no later than Friday, March 25.

SOS classes help spill responders increase their understanding of oil spill science when analyzing spills and making risk-based decisions. They are designed for new and mid-level spill responders.

These trainings cover:

  • Fate and behavior of oil spilled in the environment.
  • An introduction to oil chemistry and toxicity.
  • A review of basic spill response options for open water and shorelines.
  • Spill case studies.
  • Principles of ecological risk assessment.
  • A field trip.
  • An introduction to damage assessment techniques.
  • Determining cleanup endpoints.

To view the topics for the next SOS class, download a sample agenda [PDF, 170 KB].

Please understand that classes are not filled on a first-come, first-served basis. We try to diversify the participant composition to ensure a variety of perspectives and experiences, to enrich the workshop for the benefit of all participants. Classes are generally limited to 40 participants.

For more information, and to learn how to apply for the class, visit the SOS Classes page.


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Births Down and Deaths Up in Gulf Dolphins Affected by Deepwater Horizon Oil Spill

A mother bottlenose dolphin pushes her dead newborn calf at the water's surface.

Dolphin Y01 pushes a dead calf through the waters of Barataria Bay, Louisiana, in March 2013. This behavior is sometimes observed in female dolphins when their newborn calf does not survive. Barataria Bay dolphins have seen a disturbingly low rate of reproductive success in the wake of the Deepwater Horizon oil spill. (Louisiana Department of Wildlife and Fisheries)

In August of 2011, a team of independent and government scientists evaluating the health of bottlenose dolphins in Louisiana’s Barataria Bay gave dolphin Y35 a good health outlook.

Based on the ultrasound, she was in the early stages of pregnancy, but unlike many of the other dolphins examined that summer day, Y35 was in pretty good shape. She wasn’t extremely underweight or suffering from moderate-to-severe lung disease, conditions connected to exposure to Deepwater Horizon oil in the heavily impacted Barataria Bay.

Veterinarians did note, however, that she had alarmingly low levels of important stress hormones responsible for behaviors such as the fight-or-flight response. Normal levels of these hormones help animals cope with stressful situations. This rare condition—known as hypoadrenocorticism—had never been reported before in dolphins, which is why it was not used for Y35 and the other dolphins’ health prognoses.

Less than six months later, researchers spotted Y35 for the last time. It was only 16 days before her expected due date. She and her calf are now both presumed dead, a disturbingly common trend among the bottlenose dolphins that call Barataria Bay their year-round home.

This trend of reproductive failure and death in Gulf dolphins over five years of monitoring after the 2010 Deepwater Horizon oil spill is outlined in a November 2015 study led by NOAA and published in the peer-reviewed journal Proceedings of the Royal Society.

Of the 10 Barataria Bay dolphins confirmed to be pregnant during the 2011 health assessment, only two successfully gave birth to calves that have survived. This unusually low rate of reproductive success—only 20%—stands in contrast to the 83% success rate in the generally healthier dolphins being studied in Florida’s Sarasota Bay, an area not affected by Deepwater Horizon oil.

Baby Bump in Failed Pregnancies

While hypoadrenocorticism had not been documented previously in dolphins, it has been found in humans. In human mothers with this condition, pregnancy and birth—stressful and risky enough conditions on their own—can be life-threatening for both mother and child when the condition is left untreated. Wild dolphins with this condition would be in a similar situation.

Mink exposed to oil in an experiment ended up exhibiting very low levels of stress hormones, while sea otters exposed to the Exxon Valdez oil spill experienced high rates of failed pregnancies and pup death. These cases are akin to what scientists have observed in the dolphins of Barataria Bay after the Deepwater Horizon oil spill.

Among the pregnant dolphins being monitored in this study, at least two lost their calves before giving birth. Veterinarians confirmed with ultrasound that one of these dolphins, Y31, was carrying a dead calf in utero during her 2011 exam. Another pregnant dolphin, Y01, did not successfully give birth in 2012, and was then seen pushing a dead newborn calf in 2013. Given that dolphins have a gestation of over 12 months, this means Y01 had two failed pregnancies in a row.

The other five dolphins to lose their calves after the Deepwater Horizon oil spill, excluding Y35, survived pregnancy themselves but were seen again and again in the months after their due dates without any young. Dolphin calves stick close to their mothers’ sides in the first two or three months after birth, indicating that these pregnant dolphins also had calves that did not survive.

At least half of the dolphins with failed pregnancies also suffered from moderate-to-severe lung disease, a symptom associated with exposure to petroleum products. The only two dolphins to give birth to healthy calves had relatively minor lung conditions.

Survival of the Least Oiled

Dolphin Y35 wasn’t the only one of the 32 dolphins being monitored in Barataria Bay to disappear in the months following her 2011 examination. Three others were never sighted again in the 15 straight surveys tracking these dolphins. Or rather, they were never seen again alive. One of them, Y12, was a 16-year-old adult male whose emaciated carcass washed up in Louisiana only a few weeks before the pregnant Y35 was last seen. In fact, the number of dolphins washing up dead in Barataria Bay from August 2010 through 2011 was the highest ever recorded for that area.

Survival rate in this group of dolphins was estimated at only 86%, down from the 95-96% survival seen in dolphin populations not in contact with Deepwater Horizon oil. The marshy maze of Barataria Bay falls squarely inside the footprint of the Deepwater Horizon oil spill, and its dolphins and others along the northern Gulf Coast have repeatedly been found to be sick and dying in historically high numbers. Considering how deadly this oil spill has been for Gulf bottlenose dolphins and their young, researchers expect recovery for these marine mammals to be a long time coming.

Watch an updated video of the researchers as they temporarily catch and give health exams to some of the dolphins in Barataria Bay, Louisiana, in August of 2011 and read a 2013 Q&A with two of the NOAA researchers involved in these studies:

This study was conducted under the Natural Resource Damage Assessment for the Deepwater Horizon oil spill. These results are included in the injury assessment documented in the Draft Programmatic Assessment and Restoration Plan that is currently out for public comment. We will accept comments on the plan through December 4, 2015.

This research was conducted under the authority of Scientific Research Permit nos. 779-1633 and 932-1905/MA-009526 issued by NOAA’s National Marine Fisheries Service pursuant to the U.S. Marine Mammal Protection Act.


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How Does Oil Get into the Ocean?

Oil rig in the Gulf of Mexico.

Oil rig in the Gulf of Mexico, off the coast of Port Fourchon, Louisiana. A 2003 report from the National Academy of Sciences estimates 3% of the oil entering the ocean each year comes from oil and gas exploration and extraction activities. (NOAA)

When many of us think of oil spills, we might think of an oil tanker running aground and spilling its contents into the ocean, as in the case of the oil tanker Exxon Valdez when the ship ran aground near the coast of Alaska in 1989.

In fact, there are actually several ways crude or refined oil may reach the marine environment. All of those spills add up too. In a 2003 publication, the National Research Council of the National Academy of Sciences reported that roughly 343,200,000 gallons of oil were released into the sea annually, worldwide. Of this amount, the report estimates the origin of that oil as follows:

  • Use or consumption of oil (which includes operational discharges from ships and discharges from land-based sources): 37%
  • Transportation (accidental spills from ships): 12%
  • Extraction: 3%
  • Natural seeps: 46%

Wherever oil is consumed, such as in manufacturing or when loading a ship with fuel, there are opportunities for oil spills. According to the Washington State Department of Ecology [PDF], most spills that occur during ship fueling happen because of inattention, inadequate procedure, procedural error, or poor judgment—in other words, human error.

The typically small-in-size spills that come from consuming oil originate from a variety of activities and actually account for most of the oil spilled by humans into the sea.

When the Exxon Valdez oil spill occurred, on the other hand, crude oil was in transport. Since oil is an international commodity and in constant demand, there are always ships, pipelines, and (increasingly) trains moving it around the world. According to the International Tanker Owners Pollution Federation, occurrences of large spills from tankers and barges (above approximately 2,000 gallons) have decreased dramatically since 1970. This can be attributed at least in part to advances in safety thanks to the Oil Pollution Act of 1990.

While oil extraction is not considered a large source of the overall amount of oil released into the sea each year, spills from offshore oil exploration and drilling can be huge when they do happen. The well blowout that caused Deepwater Horizon spill in the Gulf of Mexico in 2010 is a (very large) example of an oil spill occurring during extraction activities. This type of accident occurs only where oil exploration and drilling operations take place—in the United States, the Gulf of Mexico and waters off the southern California coast are the major areas.

Dark, thick oil seeps out of the ocean floor sediments.

A natural tar seep releases oil offshore from Gaviota, California. When an oil spill occurs in an area with many naturally occurring seeps, responders may have a difficult time telling spilled oil apart from seep oil. (Donna Schroeder/U.S. Geological Survey)

While not technically “oil spills,” oil seeps from the ocean floor naturally release oil from subterranean reservoirs and represent the largest source of oil entering seas both in the United States and around the world. Even though seeps are not without their own impacts on marine life, natural oil seeps release oil slowly over time, allowing ecosystems to adapt. During an oil spill, the amount of oil released in a short time can overwhelm an ecosystem.

Impact, then, is not only determined by how much oil is in the environment, but also the type of oil and how quickly it is released.

The May 2015 oil spill at Refugio State Beach was caused by a pipeline break near Santa Barbara, California, adjacent to Coal Oil Point, a region famous for its natural seeps. Oil from seeps there release an estimated 6,500-7,000 gallons of oil per day (Lorenson et al., 2011) and are among the most active in the world. One of the response challenges during that spill was distinguishing between the oil that flowed directly into the ocean from the pipeline break and that from the ongoing seeps.

For a quick glance at the major causes of oil spills in the ocean, check out our infographic:

Graphic showing buildings and cars using oil, a tanker transporting oil, and a rig drilling for oil in the ocean, with a natural seep leaking oil out of the seafloor. Use of oil: Anywhere crude or refined oil is stored or used, such as for fuel or in manufacturing, there is risk of a spill. Transportation of oil: Crude oil is an international commodity, and as it is moved around the world, it may be spilled from storage tanks, barges, pipelines, and other bulk transport. Extraction of oil: Oil exploration and extraction from the ground or below the ocean surface potentially could release oil into the environment. Natural seeps of oil: Oil seeps are natural leaks of crude oil and gas from subterranean reservoirs through the ocean floor. While not caused by humans, oil from seeps can be confused with oil spills.

There are four primary ways oil can end up in the ocean: natural seeps, consumption, extraction, and transportation of oil. (NOAA)