MercoPress. South Atlantic News Agency

What could happen when Argentina's Sea Lion ultimatum to the UK expires

Milei ordered on September 28 the start of arbitration and said that, if London does not act, Argentina will seek provisional measures from the International Tribunal for the Law of the Sea

The two-week deadline Argentina gave the United Kingdom to halt the Sea Lion oil project in the North Falklands basin expires around October 12. Its expiry will not in itself suspend the project or establish a British breach of the United Nations Convention on the Law of the Sea, according to a legal analysis published by specialist site Diplomacy & Law.

President Javier Milei ordered on September 28 the start of arbitration under Annex VII of the convention and said that, if London does not act, Argentina will seek provisional measures from the Hamburg-based International Tribunal for the Law of the Sea. The analysis's author, Edmarverson A. Santos, stresses that the deadline was set by Argentina and does not derive from the convention, and that the government's instruction and the formal start of proceedings are separate steps: arbitration begins with written notification to the other state, accompanied by the claim and its grounds. There is no record that this has been sent.

The Annex VII route reflects both countries' choices. Under Article 287 of the convention, Argentina chose the Hamburg tribunal as its first preference and the United Kingdom the International Court of Justice; where the parties do not coincide, the dispute goes to arbitration. Beforehand, Article 283 requires an exchange of views on how to settle the dispute, something a tribunal would have to assess.

If Argentina seeks provisional measures, the Hamburg tribunal could order them while the arbitral tribunal is being constituted, provided it considers that the latter would have prima facie jurisdiction and that the matter is urgent. Such measures would be provisional, not a ruling on sovereignty or the merits.

The main obstacle is jurisdiction. Convention tribunals can only rule on its interpretation or application, not on territorial title. In the 2015 arbitration between Mauritius and the United Kingdom over the Chagos Islands, the tribunal declined to rule on a claim whose real subject was sovereignty; in the 2020 case between Ukraine and Russia, it excluded claims requiring a decision on Crimea, though proceedings continued on the rest. In addition, both countries have made declarations under Article 298: Argentina excluded maritime delimitation disputes, among others, in 1995, and the United Kingdom made exclusions in 2003 and, according to the analysis, again in 2020.

“Argentina would need to formulate claims capable of adjudication under UNCLOS without requiring the tribunal to decide, expressly or implicitly, sovereignty over the Falkland Islands,” the author concludes.

The United Kingdom rejected the arbitration on September 30 and maintains that the activity is governed by the archipelago's legislation in accordance with international law. Sea Lion, developed by Navitas and Rockhopper, has had a final investment decision since December 2025.