This book describes the specificities inherent to these two problems: accidental spillage of petroleum or petroleum products at sea ans pollution of soils and groundwater by hydrocarbons. The Author : shows that, considering the technical and financial constraints general encountered, the strategic responses brought in both cases are in fact based on the same approach involving assessment of the risks for human health and activity and for the ecosystems: this leads to the concept of net financial and environmental benefit which justifies, in some cases, the option which consists in allowing natural attenuation to take its course. This book is intended for engineers and technicians who wish to increase their knowledge of various aspects of the problems discussed, decision makers who require a better understanding of the environmental and economic stakes, as well as students and less well informed readers who will find both general and detailed information