Arbitration laws and rules rarely provide any principles for determining the applicable standard of proof. In fact, some consider this silence to be one of the strengths of international arbitration, as tribunals hold great flexibility in terms of determining the evidentiary process.

Standard of Proof in Arbitral Practice
👉In practice, the arbitral tribunal has great flexibility to determine the applicable standard of proof. The question really rests on whether arbitrators should turn to the lex arbitri or to the governing law of the merits (lex causae) to determine the applicable standard of proof. While this question can be irrelevant if the two chosen laws belong to the same system of laws, this is highly controversial whenever the lex arbitri and the governing law involve different systems of laws and different applicable standards of proof.

👉In The Burden of Proof in Arbitration, a distinction was made between the burden of proof, defined as “the duty of proving a disputed assertion or charge”, and the standard of proof, which “determines the level of certainty and the degree of evidence necessary to establish proof in a criminal or civil proceeding”, according to the Merriam-Webster Dictionary.

👉This note will focus on the latter concept: the standard of proof in international arbitration. The standard of proof defines the quantity of evidence required to establish an issue or a case, as provided by the tribunal in the Rompetrol Group N.V. v. Romania case. It is relevant because it determines the importance granted to the evidence presented by the parties.

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