The never-ending clash between the Civil Law and Common Law traditions in international arbitration took center-stage once again in 2018, with the introduction of the Inquisitorial Rules on the Taking of Evidence in International Arbitration, or the “Prague Rules”. Lawyers from the Civil Law tradition, increasingly dissatisfied with the IBA Rules on the Taking of Evidence in International Arbitration, introduced the Prague Rules as an alternative to the “adversarial approach” embodied in the IBA Rules. One key concept in the IBA Rules that has received criticism from the Civil Law tradition is that of party-appointed experts.

1. What are the problems with party-appointed experts?

Critics argue that party-appointed experts are like ‘hired guns’.[1] As they are paid and engaged by the parties and not the tribunal, the opinions of experts always support the side that hired them. The result is: arbitral tribunals obtain two conflicting expert reports that purport to be ‘neutral and objective’. As a consequence, the tribunal may lean in favour of the expert that is better able to withstand cross-examination, rather than choosing the more accurate evidence.

Another major objection raised against party-appointed experts is that they increase the length and the costs of the arbitration proceedings. Often, party-appointed experts render an opinion on questions that are either undisputed between the parties or irrelevant to the tribunal, thus leading to a waste of time and resources. Even in situations where this is not the case, party-appointed experts may utilize completely different methodologies and facts, and discuss completely different issues. This may motivate the tribunal to appoint its own expert – to evaluate the claims of the party-appointed experts, or to make a fresh and independent analysis of the issues.

2. What are the solutions to the problems posed by party-appointed experts?

While most counsel and tribunals are aware of the problems with party-appointed experts, the use of party-appointed experts is still the gold standard in international arbitration. Solutions to the problem are, in practice, often discussed with the tribunal during the case management conference and the pre-hearing conference. The parties and the tribunal very often agree on expert meetings and witness conferencing which can be considered “mild measures” to mitigate the problems. Occasionally, parties choose “drastic measures” in order to solve the problem completely.

a. Mild Measures

i. Expert meetings:

The experts are asked to meet and discuss the topics at stake before the hearing. Or better still, the experts meet and discuss even before they prepare their reports. The purpose of the meeting is that they attempt to agree on a common methodology and approach to the issues. Moreover, they are asked whether they share the same expert opinion on any of the issues at stake. If the party-appointed experts agree on a common methodology and approach to the issues, this can help streamline the arbitration proceedings. It is even better if the experts can agree on certain points, as these points then do not need to be discussed at all – either in the expert opinions or during the hearing.

ii. Witness conferencing:

Witness-conferencing (curiously termed ‘hot-tubbing’) involves the simultaneous questioning of the experts of both parties. This affords the tribunal the opportunity to pit the two experts theories against each other, rather than to evaluate them separately. Further, the expert witnesses may tend to present their findings more thoughtfully in the physical presence of one of their own. This may mitigate the perceived lack of impartiality in party-appointed experts.

A prominent English barrister, Peter Rees QC, has proposed to take witness-conferencing one step further.[2] In practice, witness-conferencing typically takes place after each expert witness is cross-examined separately. Rees proposes to proceed with witness-conferencing right from the outset where appropriate: for instance, where the tribunal has read the experts’ reports, fully understands them, and finds that they have very little in common. In such a situation, the presentation of reports by the experts and their cross-examination could be a waste of time. If the tribunal were to start with witness-conferencing, the tribunal could get to the real issues right from the beginning.

b. Drastic Measures

Where parties want to overhaul the system of party-appointed experts, they could choose between the following measures:

i. Abolish party-appointed experts altogether

The parties could agree to prohibit the use of party-appointed experts altogether and choose to exclusively avail of tribunal-appointed experts.

Neither the Prague Rules nor the IBA Rules go so far as to prohibit party-appointed experts. Therefore, this option would have to be expressly agreed upon by the parties. None of the major arbitral institutions provide this option either, and the only institution (to our knowledge) that contains such a procedure is the newly established Court of Arbitration for Art (CAA). According to its co-founders, the CAA Rules take this approach because the very purpose of the institution is the achievement of ‘decisional accuracy’ and ‘market legitimacy’. The co-founder state that the potentially ‘biased’ opinions of party-appointed experts jeopardizes the purpose of market legitimacy.

ii. Expert Teaming

Klaus Sachs, a German arbitrator, has proposed an approach to experts that he calls “expert teaming”.[3] Expert teaming is a hybrid mechanism between a tribunal-appointed expert and a party-appointed expert. The idea is that each party gets ‘its’ expert – but that expert is not appointed by the party, but by the tribunal. Under this method, the parties submit to the tribunal a list of persons (typically, 3-5 names) that they would want as experts in the dispute. The tribunal then asks each party to comment and express their objections to the persons that have been proposed by the other party. The tribunal then proceeds to appoint one expert from each list, and they form an ‘Expert Team’. Depending on what the parties and the tribunal agree, the experts can then meet with the parties individually to discuss the issues at stake. At the same time, the experts would confer with each other regularly and provide a joint report on the issues that they agree upon.

This system ensures that parties have faith in the experts appointed, as they have had a say in their appointment. At the same time, since the tribunal appoints and remunerates the experts, they will not be perceived as ‘hired guns’. Additionally, this method achieves some of the benefits of witness-conferencing, because the experts regularly discuss the issues referred to them and prepare a joint report. Further, this method also has the potential to reduce time and cost, as the tribunal would tend not to appoint a third, independent expert.

[1] Douglas Thompson, Are Party-Appointed Experts a Waste of Time? , Global Arbitration Review, available at:

[2] Peter Rees QC, Arbitration: Elastic or Arthritic, keynote speech delivered at a dinner organised by Harbour Litigation Funding for leading global firms in Hong Kong on 28th March 2017, available at:

[3] Klaus Sachs with the assistance of Dr. Nils Schmidt-Ahrendts, Protocol on Expert Teaming: A New Approach to Expert Evidence, available at: