Petroleum Inputs to the Sea: Natural Seeps is #1
There is an estimated 256,000 tons of petroleum entering North American waters every year, and 1,268,000 tons entering the marine environment worldwide. Here are the sources of the "Petroleum Inputs to the Sea," according to "Oil in the Sea III: Inputs, Fates, and Effects":
1. Natural Seeps. Natural seepage of crude oil from geologic formations below the seafloor to the marine environment off North America is estimated to exceed 160,000 tons (47,000,000 gallons), and 600,000 tons (180,000,000 gallons) globally, each year. Natural processes are therefore, responsible for 62.5 percent of the petroleum entering North American waters (see chart above), and over 45 percent of the petroleum entering the marine environment worldwide.
2. Petroleum Extraction. Activities associated with oil and gas exploration or production introduce, on average, an estimated 3,000 tons (880,000 gallons) of petroleum to North American waters, and 38,000 tons (11,000,000 gallons) worldwide, each year. Releases due to these activities, therefore, make up roughly 1.2 percent of the total petroleum input to North American waters (see chart) and 3 percent of the total worldwide.
3. Petroleum Transportation. The transportation (including refining and distribution activities) of crude oil or refined products results in the release, on average, of an estimated 9,100 tons (2,700,000 gallons) of petroleum to North American waters, and 150,000 tons (44,000,000 gallons) worldwide, each year. Releases due to the transportation of petroleum, therefore, make up roughly 3.5 percent of the total petroleum input to North American waters (see chart) and about 12 percent worldwide.
4. Petroleum Consumption. Releases that occur during the consumption of petroleum, whether by individual car and boat owners, non-tank vessels, or runoff from increasingly paved urban areas, contribute the vast majority of petroleum introduced to the environment through human activity. On average, an estimated 84,000 tons (25,000,000 gallons) of petroleum are input to North American waters, and 480,000 tons (140,000,000 gallons) are input worldwide, each year from these diffuse sources. Releases from petroleum consumption make up roughly 33% of the total petroleum entering North American waters (see chart) and 38% of the petroleum entering the marine environment worldwide.
MP: By far, the largest source of petroleum in the world's oceans is natural seepage (62.5% for North America), and the smallest source is from "petroleum extraction" (1.2% for North America). Although the percentage for "petroleum extraction" will be much higher this year due to the Deepwater Horizon oil spill, it's probably good to put this all in perspective, and consider that the transportation and consumption of petroleum contribute much higher amounts of environmental damage in a typical year than oil drilling, by factors of three times greater for oil transportation and 27 times greater for oil consumption.