Introduction
Article I of the Outer Space Treaty, 1967 (“OST”) guarantees that the exploration and use of outer space “shall be the province of all mankind” and free to all States. Article II, in the same breath, prohibits “national appropriation by claim of sovereignty, by means of use or occupation, or by any other means.” For decades these provisions coexisted without serious strain because no State or company could realistically extract and commercialise extraterrestrial resources. That changed with the rise of modern space-resource programmes, raising the question: if resources are removed from a celestial body and subsequently sold or used, does this fall within the Treaty’s freedom to “use”, or does it constitute “appropriation” i.e., is it forbidden? The Agreement Governing the Activities of States on the Moon and Other Celestial Bodies, 1979 (“Moon Agreement”) sought to address this by designating lunar resources as humanity’s common heritage and mandating the establishment of a future international framework before the start of exploitation. It failed so completely that only eighteen states have ever ratified it, none of them a major spacefaring power.
Faced with this vacuum, the United States chose not to wait for a new treaty. Section 10 of the Artemis Accords (“Accords”) takes the view that the extraction and use of space resources can be indeed compatible with the OST. It seeks to entrench this interpretation through the accumulated practice of participating States including the United States, Luxembourg, Japan, and the United Arab Emirates, who have enacted domestic legislation recognising private rights to extracted space resources. These legislative measures undoubtedly constitute relevant state practice in the application of the Treaty. The underlying premise is that if enough States consistently authorise and engage in resource activities, their conduct may help shape the Treaty’s meaning over time. The question addressed here, however, is not whether such practice exists, but whether it establishes the agreement of the Treaty parties as the concept of “subsequent practice” requires.
Particularly, two developments over the course of 2025-2026 suggest that this strategy is now colliding with a much larger and more representative body of state practice moving in a different direction and that this collision has consequences that are doctrinal and not merely diplomatic.
The Accords are plausibly understood as relying on “subsequent practice” under Article 31(3)(b) of the Vienna Convention on the Law of Treaties (“VCLT”) as its mechanism for settling the OST’s non-appropriation ambiguity. In doing so, the Accords have made a specific and testable legal claim that state practice is converging on an interpretation that permits the extraction and use of space resources. As the International Law Commission, Draft Conclusions on Subsequent Agreements and Subsequent Practice in Relation to the Interpretation of Treaties, 2018 (“ILC Draft Conclusions”) explains, not every instance of state conduct qualifies as subsequent practice under Article 31(3)(b). The practice must establish agreement regarding the interpretation of the treaty, and its interpretive weight depends upon factors including its clarity, specificity, and consistency. The central question is therefore: Does the practice generated by the Accords establish the agreement among the Treaty parties to the Outer Space Treaties as a whole, as required by Article 31(3)(b) of the VCLT?
The 2025 Draft Principles emerging from the COPUOS Working Group on the Legal Aspects of Space Resource Activities supply the clearest evidence yet that the claim has not yet been satisfied on its own terms, because the wider community of OST parties is demonstrably not converging on the reading Artemis needs. The Draft Principles are not themselves subsequent practice within Article 31(3)(b). Rather, they constitute unusually direct evidence of whether the broader community of Treaty parties shares the interpretation advanced by the Accords. Where the negotiating record itself reveals continuing disagreement over the permissibility and legal conditions of space-resource activities, it becomes difficult to argue that the agreement required by Article 31(3)(b) has already emerged.
Writing Custom Through Section 10: The Artemis Accords’ Interpretive Gambit
Section 10 of the Accords commits signatories to extract and use space resources “in a manner that complies with the Outer Space Treaty,” while affirming that such extraction “does not in and of itself constitute national appropriation.” What makes Section 10 interesting is not this assertion alone but the mechanism it explicitly invokes to make the assertion binding over time.
It is worth noting that though the Accords do not expressly invoke Article 31(3)(b), Section 10 is plausibly understood as an attempt to generate the kind of subsequent practice contemplated by that provision. The Accords reference the OST thirteen times, and Section 10 expressly commits signatories to use their experience under the Accords to “contribute to multilateral efforts to further develop international practices and rules” on resource extraction. Therefore, instead of seeking a new treaty or a formal amendment to the OST (either of which would require the kind of broad multilateral consensus that sank the Moon Agreement) the United States and its now sixty-eight signatories are attempting to establish, through repeated and consistent state conduct, that “the agreement of the parties” to the OST already supports a use-not-appropriation reading of resource extraction. If it works, no new treaty is needed: the interpretation simply becomes the settled meaning of Article II by operation of Article 31(3)(b).
The strategy is risky because Article 31(3)(b) requires evidence of agreement among the treaty parties as a whole, not merely consistent conduct by a coalition of like-minded States.
What Subsequent Practice Actually Requires
The ILC Draft Conclusions set a clear evidentiary bar. Practice under Article 31(3)(b) must establish the agreement of the parties to a particular interpretation. It is not enough that a subset of parties act a certain way among themselves. ILC Draft Conclusion does soften this in one respect: practice need not be actively shared by every party to count, since silence can constitute acceptance “when the circumstances call for a reaction.” But that qualification runs the other way when a subset of the treaty’s parties respond to a practice not with silence, but with a visible, deliberated counter-position developed in the treaty’s own dedicated multilateral forum. Active, considered non-acceptance is about as far from silent acquiescence as state conduct gets. This is the situation the Accords now face.
The COPUOS Counter-Move: Conditional Legitimacy Instead of Automatic Entitlement
While Artemis signatories have been building their practice, the UN Committee on the Peaceful Uses of Outer Space (“COPUOS”) (this is the body Section 10 names as the intended forum for multilateralising the Accords’ approach) has been doing something quite different through its Working Group on the Legal Aspects of Space Resource Activities. As detailed in previous commentaries, the Working Group’s drafts over the course of 2025 progressively moved away from treating extraction as automatically permissible under Article I’s freedom of use, and toward what the analysis calls a “conditional legitimacy” model: the lawfulness of a resource activity depends not on a blanket entitlement flowing from Article I, but on a State’s compliance with a set of multilateral principles the Working Group is still negotiating. Tellingly, the Artemis-aligned proposition that extraction does not, in itself, constitute national appropriation (i.e., the interpretive claim Section 10 is designed to entrench) appears in the Working Group’s drafts only among “possible additional provisions,” a category reserved for contested text that has not achieved consensus, rather than in the core principles.
This matters because Article 31(3)(b) asks whether there is a holistic agreement among the parties to the Treaty, not merely among a few States capable of resource extraction. COPUOS currently includes 86 of the Treaty’s 116 parties, making it a substantially more representative forum than the sixty-eight Artemis signatories. The treaty community’s own multilateral process is therefore not yet providing the agreement Article 31(3)(b) requires.
Why the Divergence Matters Doctrinally, Not Just Diplomatically
It would be easy to read this simply as two political blocs: (1) a US-aligned coalition and (2) a broader, more cautious multilateral body talking past each other, a friction which is common in any contested area of international law. However, Section 10 does not merely assert a policy preference. It identifies a claim concerning the applicable treaty regime and identifies COPUOS as the forum in which the claim would be tested and multilateralised. The Working Group’s 2025 drafts therefore are close to direct evidence on the very question Section 10 raised: whether the “agreement of the parties” to the OST supports the reading Artemis needs.
On the record thus far, it does not. This has two consequences advocates on both sides of the debate should take seriously. Firstly, for space law scholarship and practice, treating Artemis-aligned conduct as if it were well on its way to becoming settled treaty-interpretive law overstates where matters currently stand. Secondly, the commercial risk of this dispute goes further than the idea that legal ambiguity increases investment risk. Section 10 aims to mitigate that risk in so far as it converts a disputed understanding of the OST into a widely acknowledged interpretative standard through the gathering of State practices. However, Section 31(3)(b) bases the interpretative authority on whether the practice reflects the consensus of the treaty parties collectively. Prima facie, it may seem as if investment would reinforce expectations within Artemis States and make their practice more uniform over time. Nevertheless, this investment (or, the commercial significance of a practice) is insufficient and must be supplemented with a multilateral endorsement. It may be plausible that, the higher the market value of space resources, the more compelling the motivation for non-participating States to oppose an interpretation. Commercialisation, thus, reveals the effects of interpretative ambiguity as well as the amplification of circumstances in which the presence of “subsequent practice” must be evaluated.
Conclusion
None of this means the Artemis approach is wrong as policy or that a use-based reading of Article II is indefensible. Reasonable scholars disagree on that question, and the drafting history of the OST leaves room for debate. The narrower claim advanced here concerns the evidentiary requirements of Article 31(3)(b). Section 10 proceeds on the premise that the practice emerging from the Accords contributes to an agreed interpretation of the Treaty among its parties. The significance of the 2025 COPUOS Draft Principles is that it provides evidence that such agreement has not yet crystallised. On the present record, the conditions required for subsequent practice under Article 31(3)(b) remain unmet.
Possible paths to resolve this ambiguity more honestly than the current standoff could include: firstly, COPUOS’s Legal Subcommittee could use its 2026 and 2027 sessions to make an explicit finding, even a contested one, on whether Artemis-aligned practice qualifies as Article 31(3)(b) subsequent practice, rather than allowing the question to remain permanently unresolved in successive rounds of “possible additional provisions.” Alternatively, and perhaps more realistically, States seeking greater legal certainty may pursue a negotiated protocol or amendment. Unlike reliance on subsequent practice, such an approach would not depend on persuading the rest of the Treaty’s membership that a consensus already exists when the Working Group’s own drafts show, in real time, that it does not.
Whichever course is ultimately pursued, this analysis suggests a broader point. Given the increased scale of commercialisation the pressure to treat coordinated practice as settled interpretation will inevitably increase. The Draft Principles suggest that, at least for now, international law requires a distinction between the accumulation of practice and the emergence of interpretive consensus.
Navya Dhawan is a fifth year student at National Law School of India University, Bengaluru with keen interest in commercial law, technology law and space law.
Picture Credit: NASA, Artemis Accords.
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