This study examines the reporting requirements applicable in cases of events involving hazardous substances spills, and in particular fuel leaks. It includes the obligation to investigate hazardous substances events, the specification of vague concepts in regulation, confidentiality issues pertaining to the investigations and legal proceedings associated with the events, sanctions imposed for violation of the duties to report and investigate such events and the concrete arrangements applicable to industrial bodies. The study includes an analysis of the regulation in California, the European Union, Italy, the Netherlands and Germany.