The Oil Spill Information Management System (OSIMS) provides environmental, ecological, geographical, engineering, and regulatory information to bear all actors involved in oil spill research, strategic activities,and response efforts. OSIMS combines the data management capabilities of an extended relational database with facilities for data visualization, management of geographical data, and a rule-based object-oriented expert system. In this paper we concentrate on the hierarchical structure of OSIMS and we present in depth the design of its advanced visualization capabilities.