NCPA - National Center for Policy Analysis

Nature Spills The Most Oil

May 24, 2002

Surprisingly, most of the oil polluting the oceans off the coasts of North America does not come from leaky oil tankers or pipelines. In fact, most of the petroleum pollution is not due to human activities at all. It occurs naturally as seepage from the seabeds.

Based on the most accurate data available, the National Research Council found that:

  • Each year along the coasts of North America, 47 million gallons of oil seep naturally into the ocean waters from oil-containing strata beneath the seafloor -- more than 60 percent of the total.
  • By contrast, 29 million gallons of oil entering the seas come from human activities.
  • And of that number, less than 8 percent comes from tanker or pipeline spills, and oil exploration and extraction are responsible for only 3 percent.
  • Nearly 85 percent of the petroleum that enters North American ocean waters each year as a result of human activities comes from land-based runoff, polluted rivers, airplanes, and small boats and jet skis.

Other sources of oil from human activities include military and commercial jets that occasionally jettison excess fuel over the ocean and ships that release oil from their engines while in port or at sea.

The amount of petroleum released into North American and global waters is less than previously thought, the committee found. Natural seepage accounts for 45 percent of the estimated 180 million gallons released in the marine waters each year worldwide.

Source: "Oil in the Sea III: Inputs, Fates, and Effects," Committee on Oil in the Sea: Inputs, Fates, and Effects, National Research Council, 2002; Andrew C. Revkin, "Offshore Oil Pollution Comes Mostly as Runoff, Study Says," New York Times, May 24, 2002.  

For report text


Browse more articles on Environment Issues