By Facundo D. Rodriguez, Professor of International Law (University of Buenos Aires and University of San Isidro), lawyer, MA in International Relations and PhD candidate in International Law at the University of Buenos Aires.

On 19 May 2025, the International Court of Justice (ICJ) delivered its long-anticipated judgment in the case Land and Maritime Delimitation and Sovereignty over Islands (Gabon/Equatorial Guinea),[1] marking a significant milestone in the decades-long territorial and maritime dispute between the two Central African States. The case concerned the delimitation of land and maritime boundaries and the question of sovereignty over three islands: Mbanié/Mbañe, Cocotiers/Cocoteros, and Conga.

Importantly, the Court was not asked to rule directly on which State held sovereignty over the disputed territory. Instead, pursuant to the Special Agreement concluded between the Parties in 2016, the Court was requested to determine

“whether the legal titles, treaties and international conventions invoked by the Parties have the force of law in the relations between the Gabonese Republic and the Republic of Equatorial Guinea in so far as they concern the delimitation of their common maritime and land boundaries and sovereignty over the islands.”[2]

This post offers an examination of how the Court addressed the notion of title of sovereignty, focusing in particular on the conceptual and doctrinal implications of its interpretation. The analysis proceeds in two parts. The first outlines the arguments put forward by the Parties and the Court’s reasoning regarding the legal concept of title. The second situates the Court’s interpretation within the broader context of its prior jurisprudence, assessing its consistency and contribution to the evolving doctrine of territorial sovereignty.

Competing Notions of Legal Title: The Parties’ Positions

At the outset, both Parties appeared to distinguish between “legal titles” on the one hand, and “treaties and international conventions” on the other, in their respective efforts to justify claims over boundaries and sovereignty.

Equatorial Guinea advanced a broad understanding of the concept. It argued that “legal titles” are not limited to documentary evidence but encompass any legal source that can establish territorial rights. On this basis, it interpreted the Special Agreement as allowing the invocation of all relevant titles—regardless of their nature or origin—in support of its territorial and maritime claims.[3]

Gabon, by contrast, initially adopted a narrower interpretation. It asserted that “legal titles” referred strictly to documentary evidence and rejected the more expansive approach suggested by Equatorial Guinea. Although Gabon later conceded during oral proceedings that the term might include more than written documents, it nevertheless maintained that certain elements—such as state succession, the principle that “land dominates the sea,” and the principle of uti possidetis juris—fell outside the scope of what constitutes a “legal title.”[4]

On the basis of these positions, Equatorial Guinea claimed that its titles derived from succession to all territorial rights previously held by France and Spain, as well as from the 1900 Treaty and subsequent modifications thereof. As for the maritime boundary, it alos invoked the United Nations Convention on the Law of the Sea (UNCLOS), and customary international law as its legal basis.

Gabon, maintaining a more restrictive view, argued that the only valid titles relevant to land and maritime delimitation and sovereignty over the islands were the 1900 Convention and the 1974 Bata Convention.

Ultimately, the Court endorsed Equatorial Guinea’s broader interpretation. It held that the term “legal title” in Article 1 of the Special Agreement refers not only to documentary proof but also to any source of a right under international law. The restrictive definition proposed by Gabon was rejected. Nonetheless, since Equatorial Guinea did not expressly rely on effectivités or uti possidetis juris as legal titles in its final submissions, the Court declined to assess whether these elements could independently constitute such titles.[5]

The Concept of Title in Light of ICJ Jurisprudence

In reaching this conclusion, the ICJ applied its traditional broad interpretation of ‘sovereign title’. The Court reaffirmed that the notion of title encompasses both formal sources of law and any form of evidence capable of establishing the existence of a legal right. In doing so, the Court referred to its earlier holding in Frontier Dispute (Burkina Faso v. Mali) where it stated that “the concept of title may also, and more generally, comprehend both any evidence which may establish the existence of a right, and the actual source of that right”.[6]

Under this broader conception, titles of sovereignty may originate either in an expression of will that generates legal effects, or in a legally relevant fact, provided that international law recognizes it as capable of conferring sovereign rights. This dual pathway—legal act or legally qualified fact—forms the foundation of the Court’s approach in the present case.

The Gabon/Equatorial Guinea judgment thus aligns with the Court’s broader jurisprudential trend toward conceptual flexibility. It avoids a formalist reading that might exclude relevant historical or factual manifestations of sovereignty, particularly in post-colonial contexts.

However, the judgment, while addressing the issues raised by the parties, would have been much richer if it had advanced in analysing some elements that would have contributed to the understanding and application of certain principles. Most notably, the Court avoided providing a clear assessment of uti possidetis juris as a title, despite Equatorial Guinea’s early reliance on the principle as a basis for delimitation. Considering the Court’s previous practice, where uti possidetis was recognised as a general principle closely linked to the process of decolonisation and the stability of newly independent states, an analysis of this principle in its dimension as a title of territorial sovereignty would have been particularly relevant.

Considering the uti possidetis juris as the legal act through which newly independent States affirm sovereignty over the territory inherited from the former colonial power, it would be an interesting opportunity to clarify its status in international law.

A controversy related to this point arises when the Court states:

“The title that has the force of law in the relations between them […] is the title which was held by Spain[…], to which Equatorial Guinea succeeded when it achieved independence.”[7]

While the intent behind this formulation is clear, its legal expression is problematic. The title cannot remain “Spain’s,” as Spanish sovereignty ceased upon Equatorial Guinea’s independence. What is legally relevant is the effect of succession, not the colonial title itself, which at most may serve as evidence of the colonial power’s sovereignty at the critical date of territorial transfer.

This distinction between source and evidence is crucial. In accordance with prior ICJ decisions[8] colonial titles predating independence should not be viewed as sources of sovereignty, but rather as evidentiary elements that help determine the extent of the of the administered and inherited territory by the successor State; accordingly, Equatorial Guinea’s sovereignty derives from succession to Spain’s title—not from the continued existence of the Spanish title itself.

Conduct and Silence: The Role of State Behavior

Another important contribution of the judgment lies in its reaffirmation of the relevance of unilateral acts and State conduct as evidence of sovereign title. The Court noted that Gabon failed to protest Equatorial Guinea’s exercise of authority over the disputed islands following independence[9], suggesting tacit recognition.

This line of reasoning is consistent with earlier rulings. In Preah Vihear, the Court recognized that prolonged silence in the face of sovereign acts may constitute acquiescence, especially when accompanied by behavior consistent with the other State’s authority.[10] Likewise, in Pulau Ligitan and Sipadan, the absence of protest was treated as an important element in evaluating claims of effective control.[11]

The Gabon/Equatorial Guinea judgment therefore consolidates a well-established jurisprudential line: State inaction, when combined with factual control, may play a decisive role in the formation, consolidation, or even loss of territorial sovereignty.

Concluding Remarks

The ICJ’s judgment in Gabon/Equatorial Guinea represents a valuable development in the international law of territorial sovereignty. By endorsing a broad and functional understanding of “legal title,” the Court reinforces a jurisprudence that emphasizes substance over form and contextual relevance over formalistic rigidity.

While the judgment contains some notable omissions—particularly regarding uti possidetis juris and the articulation of the legal effects of succession—these do not undermine its overall contribution. Rather, they highlight areas where further clarification and doctrinal refinement remain necessary.

[1] Land and Maritime Delimitation and Sovereignty Over Islands (Gabon/Equatorial Guinea), Judgment, 19 may 2025

[2]Article 1,  Special Agreement between the Gabonese Republic and the Republic of Equatorial Guinea

Notified to the Court on 5 March 2021 by the Republic of Equatorial Guinea, p. 11

[3] Land and Maritime Delimitation and Sovereignty Over Islands (Gabon/Equatorial Guinea), Judgment, 19 may 2025, para. 37

[4] Ibid., para. 38

[5] Ibid., para. 43

[6] Frontier Dispute (Burkina Faso v. Mali), Judgment, ICJ Reports 1986, para. 18

[7] Land and Maritime Delimitation and Sovereignty Over Islands (Gabon/Equatorial Guinea), Judgment, 19 may 2025, para. 199

[8] Cfr. Frontier Dispute (Burkina Faso v. Mali), Judgment, ICJ Reports 1986; Case Concerning the Land, Island and

Maritime Frontier Dispute (El Salvador/Honduras: Nicaragua Intervening), Judgment, ICJ Reports 1992.

[9] Land and Maritime Delimitation and Sovereignty Over Islands (Gabon/Equatorial Guinea), Judgment, 19 may 2025, paras. 195-198

[10] Case concerning the Temple of Preah Vihear (Cambodia v. Thailand), Merits, Judgment of 15 June 1962, ICJ Reports 1962,  p. 6.

[11] Sovereignty over Pulau Ligitan and Pulau Sipadan (IndonesialMalaysia), Judgment, ICJ Reports 2002, p. 625