Published 14 February 2019
International law does not provide clear answers to certain questions arising in relation to common hydrocarbon deposits, i.e. deposits either located where maritime claims overlap (undelimited border deposits) or across a delimited maritime boundary (cross-border deposits). In both scenarios, States and IOCs carrying out unilateral operations may expose themselves to significant legal and practical risks. This paper explores the legal regimes applicable to undelimited border deposits and cross-border deposits respectively, including any differences between the two, to highlight areas of uncertainty and to offer some guiding principles. Specifically, this paper assesses: (i) the benefits of cooperative arrangements such as joint development agreements and unitisation agreements; (ii) whether States are under any obligation to enter into such cooperative arrangements; (iii) what States (and IOCs) can do in the absence of cooperative agreements; and (iv) legal remedies that may be available to injured States and IOCs in such situations. In particular, the authors conclude that there arguably appears to be slightly more leeway, in the absence of cooperative agreements, to conduct unilateral operations in relation to cross-border deposits than undelimited border deposits, but only in particular and limited circumstances.