This document is a supplemental brief filed by the Respondents (award creditors) before the Supreme Court of the United States, urging the Court to deny a petition for a writ of certiorari filed by the Kingdom of Spain. The underlying dispute concerns the enforcement in U.S. courts of an arbitral award rendered against Spain under the Energy Charter Treaty (ECT).

The Respondents argue that the Court should deny review because the question presented by Spain regarding the Foreign Sovereign Immunities Act's (FSIA) arbitration exception is academic. They contend that even if Spain prevailed on that narrow issue, the lower court's judgment would be upheld on the alternative ground that Spain unequivocally consented to arbitrate under the ECT, thereby waiving its sovereign immunity. The brief highlights that the United States government, in its own submission, supports this interpretation, finding that Spain gave its "unconditional consent" to arbitrate.

Furthermore, the Respondents assert that Spain's argument invoking European Union law to negate its ECT obligations is contrary to established principles of international law, specifically the Vienna Convention on the Law of Treaties, which precludes a state from using its internal law to justify non-performance of a treaty. The brief also refutes Spain's *forum non conveniens* argument, positing that no adequate alternative forum exists for enforcement. Should the Court grant certiorari, the Respondents request that it also review the broader questions of Spain's consent to arbitrate intra-EU disputes and its waiver of immunity under the ICSID Convention.