This study could not have been performed without the preparedness of many researchers and professionals around the world to share their results and experiences. The following persons in particular are acknowledged for their contributions to this report. Farzad Tahmourpour is thanked for his helpful input on oil well abandonment techniques. The authors also appreciate the assistance of Kumagai Tsukasa on translating Japanese regulations and Michael de Vos on extensive discussions on the Dutch regulatory framework on well abandonment and its implications. Margriet Kuijper and Radboud Bisschop from NAM B.V. are thanked for their discussions and permission to include data on the De Lier case study. The assistance of Richard Metcalfe, H.S. Vishwanatan, Jan Nordbotten and Yvi Le Guen is appreciated regarding reviewing and approving the reproduction of the different risk assessment methodologies. Furthermore, the report benefits from the approval of the American Petroleum Institute to reproduce sections of API Bulletin E3 and API Specification 10. Grant Lintern, Jules Schoenmakers, Tim Davies and several others are thanked for their input on well abandonment practices from their professional experiences. A special thanks to Theresa Watson for her contribution and valuable comments to the report. Finally, Neil Wildgust and Toby Aiken from IEA GHG are thanked for their support during the study.