Environmental authorities globally are challenged with the complexity of problems associated with contaminated sites. For protecting human beings and the quality of the environmental media air, water and soil, the prevention and elimination of hazards as well as impact mitigation are crucial. This manual presents information and solution-oriented procedures for all stakeholders with a focus on identification, investigation, assessment and remediation of contaminated sites at typical facilities of the oil and gas industry, such as exploration sites, tank farms and refineries. Its application shall contribute to improving the technical and administrative management and the remediation of contaminated sites.