Transportation-related sources account for most oil reported spilled into U.S. waters each year1 (box 15-C). The volume of each spill varies significantly from incident to incident: one catastrophic incident can spill millions of gallons into the environment. Consequently, the total volume of reported oil spills can fluctuate greatly from year to year (figure 15-5). For instance, transportation's share of the total volume of oil spilled between 1991 and 2001 varied from a high of 97 percent in 1996 to a low of 77 percent in 1992.
Maritime incidents are the source of most reported oil spills, particularly on a volume basis. On average, 1.8 million gallons of various types of oil were spilled each year by all transportation and nontransportation sources between 1991 and 2001. Of this, 78 percent of oil spilled came from incidents involving maritime vessels and facilities, 10 percent from pipeline incidents, and 1.5 percent from all other transportation modes (figure 15-6). Oil cargo accounted for 58 percent of the total volume spilled in 2000 .
Failures in transportation systems (vessels, pipelines, highway vehicles, and railroad equipment) or errors made by operators can result in spillage of crude oil, refined petroleum products, and other materials and cause serious damage to the environment. The ultimate impact of each spill depends on the location and volume of the spill, weather conditions, and the natural resources affected. While data exist on oil spilled into U.S. waters, there is less information available on the resulting consequences to the environment. In addition, little information exists on the quantity of oil entering the water from improper disposal of used motor oil or other nonreported sources.
1. American Petroleum Institute, Oil Spills in U.S. Navigable Waters: 1991-2000 (Washington, DC: Feb. 11, 2003).
1 When an oil spill occurs in U.S. waters, the responsible party is required to report the spill to the U.S. Coast Guard. The Coast Guard collects data on the number, location, and source of spills, volume and type of oil spilled, and the type of operation that caused the spill.