Simon Olleson > Twenty Essex > London, England > Lawyer Profile

Twenty Essex

Work Department

  • Arbitration
  • Jurisdiction, conflicts and enforcement
  • Public international law


Simon’s practice focuses on public international law and international arbitration (including both investment protection disputes and international commercial arbitration).

He has particular experience as counsel and advocate in inter-State disputes, including before the International Court of Justice (ICJ), the International Tribunal for the Law of the Sea (ITLOS) and international arbitral tribunals constituted under the auspices of the Permanent Court of Arbitration (PCA).

Simon has advised and acted in a broad range of international disputes involving: issues of State responsibility and treaty interpretation, territorial disputes, investment protection disputes (including claims before the International Centre for the Settlement of Investment Disputes (ICSID), and arbitral tribunals under the PCA and UNCITRAL Rules), issues of international human rights law, issues of sovereign immunity, disputes involving State succession, and disputes involving issues under the law of the sea (including maritime delimitation). Simon also has experience of litigation before the English courts, including cases raising issues of public international law, and matters relating to arbitration.

In addition, he has substantial experience in international commercial arbitration and has acted in cases brought under a variety of procedural rules (UNCITRAL, LCIA, ICC, Stockholm Chamber of Commerce, CIArb, etc, and covering a variety of subject matters, including sale of goods, advertising, logistics in respect of a major energy project, and a partnership dispute.

Simon also accepts appointments to sit as an arbitrator.


English (fluent); Italian (proficient); French (proficient)

Lawyer Rankings

London Bar > Public international law

(Leading Juniors)Ranked: Tier 3

Simon OllesonTwenty Essex ‘A great supporting junior, with wide experience before international tribunals. A great asset to legal teams working in this field.’