In compliance with the provisions of the Emergency Planning and Community Right to Know Act (EPCRA) of 1986, Chester County, Pennsylvania has collected information about all reported chemical releases to the environment. This paper presents an analysis of the patterns of these releases. including their composition, type, location, frequency, time and level of emergency response, over the last 12 years (1987-1999). Hydrocarbon fuels are the most frequently spilled compounds, but several extremely hazardous chemicals including sulfuric acid, chlorine, and ammonia have also been released to the environment. The patterns of hazardous materials releases in Chester County are similar to those reported in other databases at all levels: local, state, federal and international. (C) 2002 Elsevier Science B.V. All rights reserved.