In recent years there has been a likely increase in the incidence of decommissioning of offshore oil and gas installations and considerable dissension has arisen over the legal aspects of decommissioning. There is controversy as to the applicable rules of international law. There is also dissension as to adequacy of both international and state laws and practices in providing for the various interests identified by international law itself as vital to any consideration of the manner in which disused installations ought to be disposed of. The thesis therefore examines the international legal regime of the continental shelf, on which most offshore oil and gas installations are located. There is also a review of relevant principles of the law of the sea as well as other maritime zones known to international law. A comparative study is undertaken of law and practice on abandonment in six jurisdictions, selected as fairly representative of oil-producing regions of the world. Those jurisdictions are Australia, Kuwait, Nigeria, Norway, the United Kingdom and the United States. From the analysis, it hoped to ascertain representative state practice on abandonment. In view of the issue within the abandonment controversy as to whether or not Article 60(3) UNCLOS and the IMO Guidelines 1989 had become customary international law rules there is analysis of the concept of customary international law. Following that analysis, a model or paradigm is developed for use in assessing the emergence of new norms of customary international law. The objective is that the emergence of the new model will in the future enable the objective, expeditious and forthright assessment of contended rules of customary international law. The work goes further to consider whether the IMO Guidelines achieved a strategic balancing of the contending interests set out in Article 60 (3) and tries to postulate the reasons why those rules and Guidelines failed following the Brent Spar incident. Aspects of the legal-economic theory of regulatory capture are considered as apposite. The work concludes by identifying new and emerging trends in relation to abandonment practices and concludes with a postulation and as well as proposals as to how abandonment is expected to develop into the future.