Oil in the Sea: Sources
Travis Hudson, American Geological Institute, 4220 King Street, Alexandria, VA 22302

The National Academy of Science’s National Research Council (NRC) has investigated the inputs, fates, and effects of petroleum (hydrocarbon gases, liquids, and in some cases solids) released to the marine environment (The National Academy of Science’s Oil in the Sea Studies). The NRC’s most recent assessment (Oil in the Sea III published in 2003) determined that 76 million gallons of petroleum (the equivalent of almost 7 Exxon Valdez spills) are released to North American marine waters each year. These releases are principally from natural seeps, petroleum extraction operations, petroleum transport, and petroleum consumption.

Natural seeps are places where petroleum escapes to Earth’s surface from underground. On the seafloor, natural seeps release oil and gas directly to the marine environment. Such seeps are common in petroleum producing regions and were one of the first exploration guides to the presence of oil and gas resources. The NRC estimates that natural seeps release 47 million gallons or about 60% of the long term average for all petroleum entering North American marine waters each year.

Petroleum extraction operations are the activities associated with producing oil and natural gas in offshore areas. These operations include well drilling and onsite processing (most commonly to separate co-mingled or “produced water”). Petroleum leaks and discharges of produced water are sources of petroleum in the marine environment from these operations. The NRC estimates that 880,000 gallons or about 3% of the annual input to North American marine waters are released from petroleum extraction operations. The uncontrolled flow of petroleum from a well, called a blowout, is uncommon but as the April 2010 accident in the Gulf of Mexico shows, can happen. Blowouts can release as much or more petroleum to the marine environment as all other sources in a given year.

Petroleum transport from producing areas to refineries and then on to consumers is primarily by pipelines or tankers. Discharges during transport operations are commonly accidental spills such as the 1989 Exxon Valdez tanker spill in Alaska. The NRC estimates that transportation-related releases total 2.7 million gallons or about 3.5% of the long term annual average for petroleum input to North American marine waters.

Petroleum consumption-related releases include runoff of oil-bearing surface waters from urban areas, improper discharge of waste oil by vehicle and boat owners, and outboard boat engines that require mixing oil with the gasoline they burn. The NRC estimates that petroleum consumers are the source of 25 million gallons or about 33% of all the petroleum released to North American marine waters (on average) each year. This amount is nearly 85% of all the petroleum released by people to these waters each year.

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Travis Hudson

Outboard motors that mix oil with gasoline for lubrication (two stroke motors) are a source of oil in surface waters.

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Travis Hudson

Oil that drips to streets and parking lots from vehicles is a source of oil in storm water runoff. This drain for storm water is two blocks from the Pacific Ocean.

Additional Resources:
You can further investigate the NRC’s findings about the sources of petroleum in the marine environment at Oil in the Sea III. A source of general information about petroleum in the environment is AGI’s Environmental Awareness Series book Petroleum and the Environment.

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EarthNote No. 2 , © 2010-2015 American Geosciences Institute,
P. Patrick Leahy, Director, 4220 King Street, Alexandria VA 22302