Update of comparative occurrence rates for offshore oil spills

Estimates of occurrence rates for offshore oil spills are useful for analyz ing potential oil-spill impacts and for oil-spill response contingency plan ning. With the implementation of the Oil Pollution Act of 1990 (US Public L aw 101-380, August 18, 1990), estimates of oil-spill occurrence became even more important to natural resource trustees and to responsible parties inv olved in oil and gas activities. Oil-spill occurrence rate estimates have been revised based on US Outer Con tinental Shelf (US OCS) platform and pipeline spill data (1964 through 1999 ), worldwide tanker spill data (1974 through 1999), and barge spill data fo r US waters (1974-1999). These spill rates are expressed and normalized in terms of number of spills per volume of crude oil handled. All estimates of spill occurrence rates were restricted to spills greater than or equal to 1000 barrels (159 m(3), 159 kl, 136 metric tonnes, 42,000 US gallons). The revisions compared to the previously published rates calculated through 1992 (Anderson & LaBelle, 1994) indicate that estimates for the US OCS pla tform spill occurrence rates continue to decline, primarily because no spil ls have occurred since 1980. The US OCS pipeline spill occurrence rates for spills greater than or equal to 1000 barrels remained essentially unchange d. However, the rate for larger OCS pipeline spills (greater than or equal to 10,000 barrels) has decreased significantly. Worldwide tanker spill rate s, rates for tanker spills in US waters, and rates for barge spills in US w aters decreased significantly. The most recent 15-year estimates for 1985-1 999 (compared to rates for the entire data series) showed that rates for US OCS platforms, tankers, and barges continued to decline. (C) Published by Elsevier Science Ltd.