A third state is a state not a party to a treaty. The general rule is that a treaty does not create obligations or rights for a third state without its consent. Articles 35 and 36 of the Vienna Convention on the Law of Treaties elaborate the general rule by setting out the circumstances in which a treaty can apply to a third state. Before a third state can be bound by an obligation to a treaty to which it is not a party, the parties must intend the provision to establish an obligation for the third state, and the third state must expressly accept that obligation in writing. A right arises for a third state under a treaty if the parties so intend and the third state assents. The chapter discusses the application of these rules, and obligations erga omnes, defined as obligations in whose observance all states can be held to have a legal interest.

In the absence of delimitation, there are competing sets of sovereignty or sovereign rights of two States over the same area, which also imply exclusivity. This lies at the heart of why possible conflicts may occur between States. Different variants of overlapping claims can occur between States: that is, as regards internal waters, territorial seas, contiguous zones, EEZs, (extended) continental shelves and archipelagic waters. Varying with the type of disputed maritime zone involved, specific international law questions arise. Both claimant coastal States and third States can be affected by the existence of disputed maritime areas. For claimant States, questions arise around the extent to which rights can, and obligations have to, be exercised. For third States, or their nationals, questions arise concerning how to exercise rights that may have been obtained from one claimant State, and what obligations they must observe when acting, or seeking to act, in a disputed area. As State practice exemplifies, where a claimant, or a national of a third State, has undertaken unilateral conduct in a disputed maritime area, for example concerning mineral resources or fisheries, which regularly prompts the other claimant into responding – including, by taking law enforcement measures.

This chapter provides the necessary background as to why addressing the issue of the rights and obligations of States prior to delimitation is both pressing and topical. The main objective of the book is to lay out the rights and obligations of States (i.e. claimants and third States) under international law in disputed maritime areas. Particular emphasis in this regard is placed on those areas where States have not agreed upon delimitation (a), neither have been able to agree on cooperative arrangements (b), and for which a modus vivendi has not been developed to regulate activities in a disputed maritime area (c). Apart from that, States are obligated to take certain (unilateral) measures in disputed areas. This is because entitlements to maritime zones come with related obligations for the coastal State regarding certain issues. For instance, with regard to managing and conserving living marine resources, as well as protecting the marine environment, coastal States have significant obligations under the LOSC. Another issue that is discussed is how jurisdictional uncertainty, which is inherent to disputed maritime areas, affects claimant States, third States and their nationals.

The international legal framework that is applicable to disputed maritime areas consists of conventional law – predominantly found in the LOSC – and general rules of international law. Combined, these form a template of rules and obligations that must be observed by States in relation to their disputed area. Two questions arise in this regard: is the international law that is applicable in disputed maritime areas sufficiently defined? And does this international law actually contribute to prevent conflicts between claimant States, or between a third State, or its nationals, and a claimant States in respect of a disputed maritime area? Differences exist in terms of the amount of conflict that is engendered if one claimant decides to act on its rights in a disputed maritime area, without another coastal State’s prior approval. An important question is how does this aspect influence the issue of what the rights and obligations are of States in disputed maritime areas? Also, whether the scope for unilateralism can be defined conclusively is addressed. However, it becomes clear that determining this scope is made impossible by the variable of the circumstances surrounding a particular disputed maritime area.