Oil Spills
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Sources of Petroleum Entering North American Waters

Most of the estimated 29 million gallons of petroleum that enters North American waters¹ on average each year from anthropogenic sources is not the result of tanker and pipeline spills, according to a National Research Council (NRC) study. The study defined four categories of sources: natural seeps, petroleum extraction, transportation, and consumption. Among these latter three anthropogenic sources, releases that occur during consumption contribute nearly 86 percent of the petroleum that enters North American waters, while transportation contributes 9 percent (see table below).

NRC determined total consumption data by estimating releases from land-based runoff (including rivers), recreational marine vessels, spills from nontank vessels, operational discharges from vessels of 100 gross tons and less than 100 gross tons, and atmospheric deposition (including aircraft dumping). The study said that “. . . estimates for land-based sources of petroleum are the most poorly documented [of consumption data] and the uncertainty associated with the estimates range over several orders of magnitude.”

Overall, however, the study concluded that accuracy of data on petroleum releases had improved since NRC had previously reported on this issue in 1985. The study also found that the environmental effects of a major oil spill are longer lasting than once thought and even small amounts of petroleum can seriously damage marine life and ecosystems.

Sources and Estimated Annual Average Amounts of Oil Entering North American Waters

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NOTE: Percentages do not add to 100% due to rounding.

¹ North American waters include those of Canada, the United States, and Mexico.

SOURCE: National Research Council, Oil in the Sea III: Inputs, Fates, and Effects (Washington, DC:National Academy Press, 2002)