On May 19, 2025, the International Court of Justice (ICJ) gave judgment on the dispute between the Republic of Gabon and the Republic of Equatorial Guinea (the Parties) concerning “whether the legal titles, treaties and international conventions invoked by the Parties have the force of law … in so far as they concern the delimitation of their common maritime and land boundaries and sovereignty over the islands of Mbanié/Mbañe, Cocotiers/Cocoteros and Conga” (p. 8, Art. 1(1)). The judgment makes significant advances in the definition of a “treaty,” the scope of “legal title” in the law of territory, and the application of the law of state succession. It also makes an important interpretation of the 1982 United Nations Convention on the Law of the Sea (UNCLOS) as a source of law for disputes concerning maritime entitlements.Footnote ¹ The evolutionary character of the judgment also prompted multiple opinions of individual judges concerning the “colonial” basis of the case.

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By Special Agreement, the Parties recognized as applicable law the 1900 treaty between France and Spain delimiting their possessions in West Africa (para. 213).Footnote ² Gabon also invoked a 1974 Convention (Bata Convention) concerning the parties’ land and maritime frontiers.Footnote ³ They vested the Court with jurisdiction “only to determine whether the legal titles, treaties and international conventions invoked by the Parties have the force of law in their relations in so far as they concern the dispute between them” (para. 30). In deciding this narrower “dispute within a dispute,” the Court ruled on five issues: (1) the status of the Bata Convention; (2) the successions of the Parties to the territorial titles of France and Spain with respect to their land boundary; (3) the successions of the Parties to the titles of France and Spain with respect to the disputed islands; (4) the applicability of the 1900 Convention between France and Spain to the terminus of the maritime boundary; and (5) the legal force of the UNCLOS for the delimitation of the maritime boundary (para. 213). Their wider territorial dispute concerning the three uninhabited islands as well as the land and maritime boundaries thus remains pending.

The meaning of “legal titles” in Article 1(1) of the Special Agreement became a point of contention. Following debate concerning whether the Parties had intended to confine the term to conventional titles (the position of Gabon) or to include titles based on state succession and other concepts (the position of Equatorial Guinea),Footnote ⁴ the Court interpreted the term “legal title” to have “a distinct meaning that is not limited to ‘treaties and international conventions’” (para. 35). Citing its judgments dealing with the concept of legal title—Burkina Faso v. Mali Footnote ⁵ and El Salvador v. Honduras Footnote ⁶—the Court found that the term “refers to title also as the source of a right” (para. 43). In thus accepting the argument of Equatorial Guinea that titles based on state succession were admissible, the significance of this finding was in recognizing a potential source of territorial rights that was derivative rather than original. Recalling its procedural rule whereby “it is always required to rule on the final submissions of the parties,” however, the Court excluded effectivités and uti possidetis juris that had been omitted by Equatorial Guinea from its final submissions (paras. 7–8).Footnote ⁷

The Court rejected by fourteen votes to one (Judge ad hoc Pinto dissenting) the central argument of Gabon that the Bata Convention confers legal title (paras. 47, 213(1)). Purportedly signed on September 12, 1974, Gabon submitted the Convention to the United Nations Secretariat, which registered it on March 2, 2004, and then published it in the United Nations Treaty Series. Equatorial Guinea “strongly objected” to the registration of the Convention at the time; before the Court, however, Equatorial Guinea “cast doubt” on its authenticity without “formally challenging” it (paras. 28, 48, 50–53). For its part, Gabon rejoined that the copies of the Convention that it had presented into evidence were authentic and its inability to locate and present the original version of the treaty was “due to poor record-keeping” (paras. 55–56). Observing that “Gabon has not dispelled all doubts” on authenticity, the Court relied on the stance of Equatorial Guinea to “assume, without deciding, that a text was signed in Bata and that the ‘copies’ put on the record in these proceedings are reproductions” (para. 57).

Equatorial Guinea next contended that the Bata Convention did not formally qualify as a treaty in asserting that “the circumstances of its conclusion and the subsequent conduct of the Parties … show[ed]that [they] had no intention to be legally bound by it” (paras. 59–64).Footnote ⁸ Gabon averred that the Bata Convention possessed “all the characteristics of a treaty” (paras. 67–69). Citing Cameroon v. Nigeria Footnote ⁹ and Somalia v. Kenya,Footnote ¹⁰ the Court reaffirmed the customary status of the 1969 Vienna Convention on the Law of Treaties definitionFootnote ¹¹ and the centrality of intention to be legally bound amidst the “great variety of forms and designations a treaty may adopt” (para. 72). The Court found the Parties’ conduct to weigh “heavily against Gabon’s position” in providing “compelling indications that they did not conceive the ‘Bata Convention’ as a treaty with the force of law” (paras. 73, 83–96).

The Court unanimously held that “the legal titles invoked by the Parties that have the force of law in the relations between them in so far as they concern the delimitation of their common land boundary are the titles held on 17 August 1960 by France and on 12 October 1968 by Spain … to which titles Gabon and Equatorial Guinea respectively succeeded” (paras. 156, 213). Noting the Parties’ agreement that they had each succeeded to the territorial titles of France and Spain, it held the land boundary to have been delimited by Spain and France between their colonial territories (i.e., Spanish Guinea and French Gabon) in the Special Agreement of 1900.Footnote ¹² The Court was persuaded by the arguments of Gabon that modifications to the delimited boundary in the Utamboni River and Kie River areas had neither been adopted by France and Spain nor accepted by Gabon following its secession on August 17, 1960 (paras. 37–38, 46, 100–15, 116–56, 197).Footnote ¹³

The Court unanimously held the 1900 Convention to constitute a “legal title … to the extent that it has established the terminus of the land boundary … [as] the starting-point of the maritime boundary” and the UNCLOS to have “the force of law … in so far as that Convention concerns the delimitation of [the] maritime boundary” (para. 213). Rejecting the submission of Gabon, the Court cited Somalia v. Kenya for the 1900 Convention land boundary terminus but also held the customary principle that “the land dominates the sea” to “not itself [be] the source of a right to specific maritime areas” (paras. 200–04, 210–12).Footnote ¹⁴ Finally, the Court held that the UNCLOS can be “relevant to the delimitation of the Parties’ maritime boundary” yet “does not constitute a legal title within the meaning of … the Special Agreement” (para. 211).Footnote ¹⁵

Separately, the Court held there to have been no treaty establishing title to the three disputed islands. Applying international law on the acquisition of territorial title, it held France to have recognized the island of Baynia (Mbanié/Mbañe) in 1886 and 1887 as a “geographical dependenc[y]” and “natural dependenc[y]” of Corisco Island over which Spain had established title from 1843 (paras. 185–91). As the Parties had agreed that the three islands were a single unit, the Court accepted by thirteen votes to two (Judge Xue and Judge ad hoc Pinto dissenting) the claim of Equatorial Guinea to the islands in succession to Spain which “as a colonial power, held title … based on an intentional display of authority that was continuous and uncontested” (paras. 198, 213).

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The judgment is significant for the development of international law in three respects: (1) interpretation of special agreements on the limits of the Court’s jurisdiction and the admissibility of legal claims; (2) authentication and status of documents claimed to be “treaties”; and (3) succession of states, especially decolonized states, to territorial titles of their predecessors. As each of these issues concerns general international law, the reasoning of the Court can find application in contexts other than the immediate one of a classical dispute concerning land, maritime and insular territory. While the judgment also leaves important questions open, it thus marks an important step in the doctrinal evolution of the law.

On the first issue of jurisdiction and admissibility, the decision offers negotiators who draft special agreements important guidance on the definition of the dispute submitted to its jurisdiction (“framing the question”).Footnote ¹⁶ While the novel formula adopted by Equatorial Guinea and Gabon differed from those employed in other cases (e.g., “what principles and rules of international law are applicable”Footnote ¹⁷ and “determine the legal situation of the islands and maritime spaces”Footnote ¹⁸) the debates seen in these proceedings concerning the limits of the Court’s jurisdiction to decide the “dispute within a dispute” contrast with other cases in which disputing parties vest the Court with full power to award territory by adjudicating the wider territorial dispute.Footnote ¹⁹

Citing Burkina Faso v. Mali Footnote ²⁰ and El Salvador v. Honduras,Footnote ²¹ the Court also made an important interpretation of the Special Agreement in stating that legal title “refers to title also as the source of a right” (para. 43). In the written phase, Gabon had distinguished between “cause of title,” “proof of title,” and “mode of title” in arguing that the legal title was confined to “proof of title” because “the title claimed is supported/demonstrated by a document with an intrinsic value under international law.”Footnote ²² In the oral phase, however, Gabon appeared “to have conceded that the term ‘legal titles’ embraces more than documentary evidence” but contended that state succession and uti possidetis iuris fall outside any definition because their function is “not to create but rather to transfer a pre-existing title” (para. 38).Footnote ²³

Finding the legal term of art in the Special Agreement to have been intended to align with general international law, the Court’s broad interpretation of “legal title” as embracing a wide range of claims carries important implications for other pending territorial disputes (para. 43).Footnote ²⁴ Unless disputing parties adopt a different definition in special agreements, the default position appears to be that the term “legal titles” embraces the full range of sources or bases of title that can be advanced in support of their territorial claims.

On the second issue concerning the authenticity and status of the Bata Convention, the nuanced conclusion of the Court is explicable in the drafting context of the judgment. In electing to focus upon the “decisive” issue of its status as a treaty, its conclusion on existence and authenticity does not develop its jurisprudence on the standard of proof in the absence of an original document (paras. 57–58).Footnote ²⁵ In particular, it is not clear whether the document held in the archives of France carried sufficient corroborative weight to meet the requisite standard of proof.Footnote ²⁶ In contrast, the analysis of the Court on the role of subsequent conduct provides states and their legal advisers with guidance—at least, for those governed by the modern law of treaties—to inform their policies concerning their status and content in practice. Vagueness concerning the status of agreements as a treaty is not rare.Footnote ²⁷

On the third issue of state succession to territorial title, the Court provided the clearest exposition to date on this sensitive area of law which concerns not only the territorial entitlements of decolonized states but also the legal basis by which they came into being during decolonization (paras. 21, 25, 111, 122, 128, 136, 141, 151, 161).Footnote ²⁸ Its clear finding that Gabon and Equatorial Guinea succeeded to the territorial titles held by France and Spain is consistent not only with prior judgmentsFootnote ²⁹ but also state practice and opiniones juris on succession to territorial claims.Footnote ³⁰

In his separate opinion, Judge Yusuf took issue with “the continued use by the Court, and sometimes by the African States themselves and their counsel, of colonial-inspired or devised terminologies as well as notions and principles of colonial law.”Footnote ³¹ He pointed to “the nature and legal value of agreements between a State and local chiefs”Footnote ³² and the interpretation of agreements between the United Kingdom and the Kings and Chiefs of Opobo and Old CalabarFootnote ³³ as being “‘not an agreement between equals’ but rather ‘a form of internal organisation of a colonial territory, on the basis of autonomy of the natives.’”Footnote ³⁴ This is linked to a longstanding problem of evincing and interpreting such agreements,Footnote ³⁵ which in Cameroon v. Nigeria was shown by the difficulty to prove the international legal personality of Old Calabar after 1885.Footnote ³⁶ The conundrum faced by African states on uti possidetis juris was also lamented in the separate opinion of Judge Tladi.Footnote ³⁷

The continued reliance of African states upon legal doctrine recognizing these effects may be attributed in part to the fact that many, if not most, are creatures of colonization.Footnote ³⁸ While the version of uti possidetis juris adopted by Organization of African Unity differs from that used by the successors to Spain in Central and South America,Footnote ³⁹ the application of colonial law to resolve intra-African territorial disputes rests on the positive law adopted by African states themselves.

Though an important judgment for the doctrinal development of general international law and its wider implications for the legal understanding of decolonization, it provides the Parties for the immediate dispute with their legal starting point for their negotiations (para. 5). This was remarked in a public address delivered by the co-agent of Gabon before the president of Gabon and other statesmen.Footnote ⁴⁰ Though identifying the land boundary delimited in the 1900 Convention as their starting point, the Parties can modify it. In stating the UNCLOS to have the force of law, the judgment implies that dispositive principles of maritime delimitation (i.e., the three-step methodology in Black Sea Footnote ⁴¹) are to guide negotiation.

However, the Court’s treatment of title to the three islands leaves open the definition of “dependencies” in general international law. Though holding the islands to have been “dependencies” of Corisco Island, it considered it not to be necessary to “establish a definition of the notion of ‘dependencies’ under international law”—a point that also arose in Malaysia v. Singapore.Footnote ⁴² Unlike its reliance on subsequent conduct to buttress its conclusion on the Bata Convention, its refusal to define dependencies in general international lawFootnote ⁴³ indicates a lack of agreement on that point amongst the majority.

Title to these uninhabited features appears to be significant less for their intrinsic value than for their potential impact on the maritime boundary for the division of natural resources.Footnote ⁴⁴ Though described as “islands” in the Special Agreement, the use of the term without prejudice to their legal character is significant insofar as the effect of any maritime zones, including baselines, generated by “islands” versus “rocks” (or even “low tide elevations,” given a surface area of 0.003 km² at high tideFootnote ⁴⁵) is concerned. While the judgment thus sets the negotiating table, it thus leaves considerable scope for the Parties to rearrange it in the framework of comprehensive bargaining on all issues.