Keith and Porricelli point out that the volume of oil pollution caused 

 by a grounding is likely to be three to four times that expected from a 

 collision, primarily because of the tendency to hole many tanks during a 

 grounding, often leading to the total loss of a vessel and its cargo. In 

 their analysis, they found that the smallest tankers (10,000 to 20,000 dead- 

 weight tonnage) were responsible for the highest relative frequency and 

 magnitude of oil pollution incidents, and that the very large cargo carriers 

 (200,000 deadweight tonnage) were' responsible for much less pollution per 

 deadweight ton afloat than the average tanker. The Argo Merchant carried 

 about 27,000 tons. Keith and Porricelli' s (1973) analysis of the vintage of 

 tankers involved in accidents showed that vessels over 17 years old were 

 responsible for more than their share of accidental pollution Incidents, and 

 about half of those were due to structural failures. The Avgo Mevohant was 

 23 years old when it ran aground on Nantucket Shoals. 



In 1970, the Dillingham Corporation carried out a study of the "major" 

 oil spills that had taken place worldwide between 1955 and 1970. Seventy- 

 five percent of the major incidents that took place during those 15 years in- 

 volved vessels, and 90 percent of the vessels involved were tankers. In that 

 study, it was concluded that the likely source of a major spill in the United 

 States coastal waters would be an oil tanker carrying crude oil or residual 

 fuel. Because of the high traffic in and around port facilities, it was also 

 predicted that major spills will most often occur within 10 miles of shore 

 and within 25 miles of the nearest port. The Dillingham report predicted 

 that the median volume of a major spill would exceed 5,000 barrels, the 

 median size spill in the 1955-1970 period being 25,000 barrels. The Argo 

 Merchant spill, on the high side of that estimate, comes in at 189,000 bar- 

 rels. 



Since the U.S. Coast Guard began its Pollution Incident Reporting System 

 (PIRS) in 1971, it has been possible to examine oil spills in U. S. waters in 

 substantial detail. For the three years in which breakdowns by spill size 

 are available (1972, 1974, 1975), there were an average of only 24 spills per 

 year that exceeded 100,000 gallons (2,381 barrels) in size. These 24 "major" 

 oil spills per year constituted only 0.3% of the total number of spills, but 

 produced twothirds (68.7%) of the total oil pollution each year, averaging 

 about 11,400 barrels per spill. The PIRS reports also indicate that, during 

 the 1971-1975 period, oil tankers and tank barges were responsible for dis- 

 charges averaging 116,139 barrels per year or 29% of the average annual 

 total each year; that crude oil and residual fuels accounted for 60% of all 

 of the petroleum pollution in the United States during 1973-1975 (crude oil 

 alone, 49%); and that spills in ports, coastal estuaries, bays and sounds, 

 and non-navigable waterways accounted for 87% of the total oil discharged in 

 1971-1975. The PIRS reports do not completely account for oil spills in the 

 contiguous zone or on the adjacent high seas. 



For all practical purposes, it appears that the predictions made by 

 Dillingham Corporation in 1970 remain true to this day. The Argo Merchant 

 oil spill was neither particularly unusual nor unexpected. The volume of oil 

 discharged (189,000 barrels) can be considered somewhat exceptional, but the 

 nature of the accident was not unusual. The Argo Merchant accident was a 



