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Natural Seeps and Oil Spills

Although it comes from a natural source, oil from natural seeps shows similar appearance, behavior, and effects as oil released during drilling and other human activities. As a result, oil from seeps affects fish, birds, and wildlife; can impair surface waters and shorelines; and can impact recreational activities.

Boats skimming oil off the ocean surface.
Cleaning up an oil spill in an area known for having abundant natural seeps, such as the waters off southern California, can be a complicated process. (NOAA)
How Can Seep Oil Be Distinguished From Spilled Oil?

Natural oil seeps are a confounding factor when determining the source of oil (via a process known as "fingerprinting") during an oil spill. Once in the ocean, some spilled oil can become co-mingled with oil originating from natural seeps, further complicating the matter. Oil seeps stem from oil fields underneath the seafloor. Oils extracted from these formations may be chemically similar to seep oil, but oil coming from seeps is often more degraded and weathered than spilled oil. One way to identify seep oil in the ocean is by the consistent pattern of surface expression, which can be traced back to the source from the air. Slicks of seep oil may also be associated with bubbling of natural gas at the ocean surface.

What Are the Impacts of Seep Oil?

Oil from seeps can be toxic to marine life, including fish, sea stars, and shrimp, largely in the immediate seep area. According to a 2014 study by Henkel et al., more than 1,000 birds each year are oiled in southern and central California, primarily due to natural seeps. Tarballs from seeps washing up on beaches can be a nuisance to beachgoers, while boaters moving through slicks from natural seeps may detect noxious odors.

More Information About Seeps

How Does Oil Get into the Ocean? While spills from oil tankers might come to mind first, there are actually several ways oil can reach the marine environment, including natural seeps. Check out our infographic showing the major ways oil ends up in the ocean.

What is an Oil Seep? An explanation of oil seeps, provided by NOAA's National Ocean Service.

Last updated Wednesday, November 22, 2023 11:52am PST