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Expert evidence in International Arbitration: The role of experts and use of expert evidence

05 December 2022

Expert evidence is used in international arbitration to assist tribunals on matters outside the arbitrators' expertise.  It is important, therefore, that the evidence is provided in a way which is procedurally helpful, and in a manner appropriate to the needs of the tribunal.

In this second article on expert evidence in international arbitration, Katherine Doran and Iona Hamilton consider how parties and the tribunal can obtain maximum benefit from expert evidence, looking in particular at the role of experts, and how evidence can be delivered to best effect.

The Role of Experts

Early Involvement

It is convenient to think of experts as falling into one of two categories: (1) a testifying expert, who provides an independent opinion to the tribunal, and (2) a consulting expert, who may be involved in assisting parties to draw up claims and advance positions.  The latter are hired guns, advocating on parties’ behalves, with no suggestion of independence or impartiality. These 'dirty' experts could not be used at tribunal as their independence would be compromised.

It is essential, therefore, that clear instructions are provided to experts, clearly setting out their role and responsibilities.  It is helpful to set out the questions which an expert is asked to consider, and the factual evidence on which they are to rely.  Note that tribunals may ask for disclosure of instructions to testifying expert witnesses. 


In arbitration proceedings, experts will always be required to produce a written report.  Reports may be exchanged at the same time of statements of case or defence if memorial style pleadings are used.  In other cases, the expert reports may be exchanged later, after document production and exchange of factual witness statements. 

Expert reports must state very clearly what facts and assumptions are relied upon. It is not for the expert to give factual evidence in their report.

Care should be taken to avoid duplication of evidence of experts of similar disciplines.  This may result in the tribunal ordering overlapping sections of a report to be struck out. This can slow down the procedure and increase parties costs, as well as looking bad from a presentational point of view.

Scope of Dispute

Experts can play a crucial role in helping to define and narrow the issues in dispute. This can be done through expert meetings.  These meetings are not attended by the parties or their representatives, rather by a group experts of a similar discipline who meet to talk through the issues and try to find areas of agreement, and identify the key issues in dispute. The outcome of this meeting can then be captured in a joint statement or joint list of issues, and can help to frame the hearing.

At the Hearing

Clearly the expert has a significant role to play at the hearing itself. This is the chance for parties to present their evidence, and test that of their opponent. Expert evidence is obviously an important part of this. During the hearing, the expert should remember that their duty is to the tribunal and not their instructing party.

Ensuring Expert Evidence has Maximum Effect

Optimised Procedure

Ideally, arbitration procedure should allow sufficient time for experts to meet and try to narrow the issues in dispute.  This should not be seen as a tick box exercise in the weeks running up to the hearing.

The parties and the tribunal may also agree a protocol for the use of expert evidence.  This may include a list of questions to be addressed by experts for both sides, or a requirement that reports be limited to specific questions or issues. The parties may also want to agree arrangements for the release and sharing of test results or analyses.


It is essential that experts are able to convey their evidence in a manner which can be clearly understood by a tribunal.  This will involve explaining extremely complex and technical issues in a clear and succinct manner. 

There are a number of tools at an expert's disposal to ensure their evidence is understandable, interesting and engaging. Pictures and diagrams should always be used, as well as use of technology, such as videos or animations.

Frankness, Honesty and Impartiality

Experts must be clear about their experience and background.  If a matter is outside an expert’s expertise, they should say so. Experts should avoid presenting their opinions as facts, making unsupported assumptions, or relying on matters which are not in evidence.  


Arbitrations can run for years.  Experts need to ensure that they regularly refresh their minds of their evidence, and the facts upon which their opinions are based.

Compelling Testimony

Expert evidence can make or break a case, so it needs to be clear, compelling and persuasive.  There are ways to facilitate this, such as inviting experts to make short, succinct presentations at the outset of their testimony.  This can be particularly helpful if the presentation is supported by graphics and may be more compelling than an expert being led in chief.  Hot tubbing is another great example, where a discussion between the experts can really help to capture the nub of a dispute.


If you are involved in a project, and it looks like a dispute may arise, please speak to us. We can advise on the need for expert evidence, and help to identify suitable experts, with the necessary skills and experience. We can guide you through the process, and ensure that expert evidence is provided in a way which will be of maximum benefit to the tribunal.

Authors: Katherine Doran and Iona Hamilton

Further Reading