Offshore exploitation of oil and gas started in the 1930s and thousands of installations are distributed around the world. Offshore installations threaten the environment, not only when it comes to oil spills, which are most visible but admittedly rare, but also in relation to their contribution to marine debris, pollution by dumping and greenhouse gas emissions. Nonetheless, the construction, operation and decommissioning of offshore installations, in the energy sector and beyond, is one of the maritime economic activities that has not yet been comprehensively regulated at the global level. The relevant international legal framework consists of a plethora of instruments adopted at the global, regional and supranational level, which have developed in different institutional settings and following different formats. The result is that, first, there is no specialised framework convention and consequently, the legal framework is fragmented at the sectoral, institutional, geographical and issue-related level. Second, the legal framework is weak because of the non-binding nature of many of the instruments that are the outcome of unconventional lawmaking1 processes. Third, the lawmaking processes in this field seem to be industry-led because of the important role the industry plays in unconventional lawmaking, both within and outside conventional fora.2 While unconventional lawmaking processes guarantee flexibility and the needed timeliness of regulatory efforts for a sector in continuous development and expansion, they do not necessarily allow for safeguarding or constructing the coherence of the legal framework. Moreover, the processes might be abused to push forward the agenda of the strongest actors, at the expense of global commons such as the marine environment and climate. In order to support these submissions, the present chapter will proceed in four steps. First, it will briefly introduce the existing conventional legal framework and highlight its fragmentation at the material and geographical levels. Special attention will be dedicated to the mechanisms for the further development of the law contained in the analysed instruments, e.g. rules of reference and monitoring mechanisms. Second, the analysis will concentrate on unconventional lawmaking performed by conventional actors, namely competent international organisations and treaty-bodies, with a focus on the standards for the conduct of environmental impact assessment. Third, the chapter will analyse the role of private actors, namely the industry, in unconventional lawmaking. Self-regulation plays an important role in the offshore energy sector. Codes of conducts adopted by multinational corporations, guidelines and recommendations drafted by professional associations highly influence the legal framework, also at the international level. A special mention will be made here to the renewable energy sector and the role of the International Renewable Energy Agency (IRENA) as an example of an industry-led international organisation that has only produced unconventional law so far. Fourth, the legal nature of the outcomes of unconventional lawmaking will be analysed in light of their relationship to the existing conventional instruments. Specifically, it will be considered whether the unconventional lawmaking in the offshore energy sector has an autonomous normativity or whether their ‘being law’ derives from their interpretative function of applicable binding instruments. Some concluding remarks will be presented in order to highlight how unconventional lawmaking contributes to the fragmented and weak nature of the existing international legal framework. Seline Trevisanut (PhD, University of Milan; MA, Paris I-Panthéon Sorbonne) is Professor of International Law and Sustainability at Utrecht University since 2018. She joined Utrecht University in 2012 as Marie Skłodowsk...