I. INTRODUCTION
International commercial arbitration is a frequently used method for the resolution of complex disputes requiring technical expertise. In such disputes, it is crucial for the arbitral tribunal to obtain clarification on issues requiring specialized knowledge to render an accurate and fair decision. As a result, arbitral tribunals often appoint an independent and impartial expert to prepare a report on specific matters. Although the expert’s report is an important tool for the tribunal, accepting it as the sole and absolute truth would conflict with the fundamental principles of adversarial proceedings1 and the right to a fair trial.
At this point, the parties’ right to question the assumptions, methodology, and conclusions contained in the Expert’s report emerges as a procedural safeguard. This right allows the parties to test the accuracy and reliability of the report and to effectively present their claims and defenses against it. In addition to examining their own appointed experts (“Party-Appointed Experts”), the ability to question the Expert—who is perceived as a neutral element of the proceedings—enhances transparency and accountability.
However, the procedure, scope, and practical challenges of exercising this right vary across different arbitral rules and traditions. This brief aims to analyze the parties’ right to question the Expert in international arbitration, examining its theoretical basis, its treatment under major institutional and practical instruments, modern practical techniques such as “hot-tubbing” and “shadow experts,” and practical issues arising in the process.
II. PROCEDURAL SAFEGUARDS GOVERNING THE EXAMINING OF EXPERTS
The parties’ right to question the Expert is not merely a positive rule found in certain arbitral instruments; rather, it is a natural consequence of the right to a fair trial and the adversarial principle. These fundamental principles require that the parties be given the opportunity to comment on and test any evidence presented against them. As the expert’s report constitutes evidence, the parties must be allowed to challenge it and question the expert who prepared it.
Doctrine notes that where no alternative expert evidence is submitted, tribunals tend to rely more heavily on the Expert’s opinion2. This situation creates the risk that the arbitral tribunal’s decision will be largely based on a single technical opinion in a scenario where the expert cannot be questiond. The parties’ right to question the expert prevents such “single-authority” dependence, enabling the report to be questiond from different perspectives and subjected to critical scrutiny. This process enhances the expert’s accountability and encourages greater diligence, impartiality, and accuracy in the preparation of the report, as the expert knows that any deficiency, flawed assumption, or potential bias may be exposed during examining.
Therefore, granting the parties the right to question the expert’s report allows them to participate actively at every stage of the proceedings, reinforcing the legitimacy of the arbitration process and the fairness of the final award.
III. THE EXAMINING PROCEDURE UNDER THE RULES OF MAJOR INSTITUTIONAL ARBITRATION CENTERS AND THE IBA RULES ON THE TAKING OF EVIDENCE
1. International Chamber of Commerce (ICC) Arbitration Rules
The International Chamber of Commerce (“ICC”) arbitration rules are among the most widely used institutional arbitration rules in the world. Article 25(3) of the ICC Arbitration Rules contains the provision: “The arbitral tribunal, after consulting the parties, may appoint one or more experts, define their terms of reference and receive their reports. At the request of a party, the parties shall be given the opportunity to question at a hearing any such expert.”. This provision establishes the parties’ right to question as an explicit procedural safeguard.
2. London Court of International Arbitration (LCIA) Arbitration Rules
Article 21(4) of the London Court of International Arbitration (“LCIA”) Rules grants the arbitral tribunal the authority to order the Expert to attend a hearing upon the request of a party or if the tribunal itself deems it necessary: “If any party so requests or if the Arbitral Tribunal considers it necessary, the Arbitral Tribunal may order the expert, after delivery of the expert’s written report, to attend a hearing at which the parties shall have a reasonable opportunity to question the expert on the report and to present witnesses in order to testify on relevant issues arising from the report.”. Although this regulation seems to grant discretion to the Arbitral Tribunal, this discretion must be exercised within the framework of fundamental principles such as due process and equality of arms. In practice, a reasonable request for examining made by a party is generally accepted by arbitral tribunals.
3. Istanbul Arbitration Centre (ISTAC) and Istanbul Chamber Of Commerce Arbitration and Mediation Center (ITOTAM) Rules
The provision in Article 29(3) of the Istanbul Arbitration Centre (“ISTAC”) Rules, “The Sole Arbitrator or Arbitral Tribunal may hear the experts appointed by the parties, as wellas, after consulting with the parties, if it deems necessary, may appoint an expert and define the scope of duty. At the hearing, the Sole Arbitrator or Arbitral Tribunal or the parties, may directly ask questions to any such expert(s).”, explicitly regulates that parties may directly question Experts at the hearing. A similar approach has been adopted in the Rules of the Istanbul Chamber of Commerce Arbitration and Mediation Center (“ITOTAM”). Article 35(2) of the ITOTAM Arbitration Rules grants the parties and the arbitral tribunal the authority to question experts or specialists at the hearing: “The parties and the arbitral tribunal may question the experts or specialists at the hearing.”. These regulations demonstrate that Turkish arbitration institutions have also adopted modern international practices.
4. United Nations Commission on International Trade Law (UNCITRAL) Arbitration Rules
Article 17(3) of the UNCITRAL (“United Nations Commission on International Trade Law”) Arbitration Rules makes it mandatory for the arbitral tribunal to hold a hearing for the presentation of evidence if requested by a party3. The examining of expert evidence is also evaluated within this scope. Article 29(5) of the UNCITRAL Arbitration Rules contains the following provision regarding the right to question: “At the request of any party, the expert, after delivery of the report, may be heard at a hearing where the parties shall have the opportunity to be present and to interrogate the expert. At this hearing, any party may present expert witnesses in order to testify on the points at issue.”. With this rule, if a decision is made to hold a hearing, the right of the parties to question the Expert and to have their own expert witnesses heard is guaranteed. This regulation confirms that this right is a fundamental safeguard for ad hoc arbitrations as well.
5. International Bar Association (IBA) Rules on the Taking of Evidence
The IBA Rules on the Taking of Evidence in International Arbitration (“IBA Rules of Evidence”), which set the framework for the taking of evidence in international arbitration practice, contain the most detailed and guiding provisions on this subject. These rules aim to establish a common and predictable standard of evidence among parties from different legal systems.
The examining of the Expert is regulated in Article 6(6) of the IBA Rules of Evidence as follows: “At the request of a Party or of the Arbitral Tribunal, the Expert shall be present at an Evidentiary Hearing. The Arbitral Tribunal may question the Expert. The Parties or any Party-Appointed Expert may question the Expert on issues raised in his or her Expert Report, the Parties’ submissions, Witness Statements or the Expert Reports made by the Party-Appointed Experts pursuant to Article 6.5.”.
This provision is distinct from other rules in that it allows the Expert to be questiond directly not only by the parties but also by the Party-Appointed Experts. This is a highly effective method that facilitates reaching the substantive truth by enabling experts to question each other directly, especially on complex technical issues. It is accepted in doctrine4 that the term “shall” in the original English text of the provision is of a mandatory nature and does not grant discretion to the arbitral tribunal5. This means that if a party so requests, the Expert’s attendance at the hearing and examining are mandatory.
IV. PRACTICAL METHODS OF EXAMINING
1. Examining Methods: Cross-Examination and Expert Conferencing (Hot-tubbing)
Traditionally, especially in the common law legal tradition, the examining of a witness or expert is conducted through the “cross-examination” method. In this method, the opposing counsel asks leading and challenging questions to expose inconsistencies, weaknesses, and assumptions in the Expert’s report. While this method is highly effective for testing the reliability of evidence, it has a time-consuming and adversarial nature.
In recent years, especially in technical and complex disputes, a more collaborative method called expert conferencing (Hot-tubbing) has gained popularity as an alternative6. In this method, Party-Appointed Experts and the Expert are brought together at the hearing simultaneously. Under the moderation of the arbitral tribunal, the experts discuss each other’s views within a specific agenda, ask each other direct questions, and interactively clarify points of disagreement. This forum-style discussion provides a more efficient, less adversarial, and more effective environment for reaching the substantive truth compared to classic cross-examination. This method is considered beneficial in terms of efficiency and due process in arbitrations with multiple expert opinions. Indeed, the Witness Conferencing in International Arbitration Guidance Note published by the Chartered Institute of Arbitrators (CIArb) in 2019 encourages the use of this method in cases with multiple experts; it is even stated that in some practices, expert conferencing has become the default method7.
2. The Role of Experts Advising the Party Counsel: The “Shadow Expert” Role
In international arbitration, a party may resort to expert evidence in two different ways. The first is the “Party-Appointed Expert,” who submits a report and testifies at the hearing. The second is the “consulting expert,” or commonly known as the “shadow expert,” who provides strategic and technical support to the party’s counsel during the preparatory phase of the proceedings but does not testify at the hearing.
The Expert’s report often contains complex technical analyses. It may not always be possible for party counsel to fully understand these analyses, evaluate them critically, and prepare the right questions for an effective examination. This is where the shadow expert comes in. This expert works as part of the party’s legal team, and their duty is not to the arbitral tribunal but directly to the party that appointed them. Therefore, their work is generally protected under attorney-client privilege.
The shadow expert analyzes the report prepared by the Expert, identifies methodological errors, deficiencies, or weak assumptions in the report, and guides the party counsel in preparing technical questions to be asked to the Expert. This method allows the party counsel to effectively test the Expert with the support of their own expert, without getting bogged down in technical details8. Although it creates an additional cost, the use of a shadow expert is considered a highly useful and established practice for parties to present their claims in the strongest possible way and to fully exercise their right to a fair trial.
V. PRACTICAL CHALLENGES AND SOLUTIONS
1. Cost and Time Management
Resorting to expert evidence, especially when multiple experts are involved in the process, can significantly increase arbitration costs and the duration of the proceedings. Lengthy cross-examinations or preparatory processes can undermine the speed and cost-effectiveness that are among the primary advantages of arbitration.
Arbitral Tribunals should exhibit effective case management from the very beginning of the process. The stages related to expert evidence (submission of reports, replies, hearing) should be clearly defined in the procedural timetable, and these timelines must be adhered to. The use of more efficient methods, such as “expert conferencing,” should be encouraged instead of classic cross-examination. The duration of examining can be reasonably limited in proportion to the complexity of the subject matter.
2. Concerns Regarding Independence and Impartiality
It is essential that the expert appointment process is conducted transparently. The arbitral tribunal should seek the parties’ views when identifying potential expert candidates and share the candidates’ declarations of independence and impartiality with the parties. The parties should be given the opportunity to present reasonable objections to the candidates. The examining phase should also be seen as an opportunity to reveal any potential prejudice or bias of the Expert.
3. Risk of Exceeding the Scope of Examining
Parties may abuse the right to question by going beyond the limits of the expert report to introduce new claims or to harass the other party. This can cause the proceedings to deviate from their purpose and be unnecessarily prolonged. The arbitral tribunal should maintain control of the process by taking an active role during the examining. The tribunal should intervene in questions that exceed the scope of the proceedings, are irrelevant, or are repetitive.
VI. CONCLUSION
The right of parties to question the Expert in international commercial arbitration is an indispensable part of modern arbitration law. This right is a concrete manifestation of fundamental procedural safeguards such as due process, the adversarial principle, and equality of arms9. The rules of major international arbitral institutions such as the ICC and the LCIA, as well as those of prominent national institutions such as ISTAC and ITOTAM, along with the widely used IBA Rules on the Taking of Evidence, unequivocally recognise the existence of this right. The UNCITRAL Arbitration Rules, for their part, protect the right to question as a fundamental safeguard.
In practice, modern and collaborative methods such as “hot-tubbing” and the use of “shadow experts” have been developed for the effective exercise of this right. These methods, on one hand, increase the efficiency of the proceedings and, on the other, allow parties to understand complex technical issues more deeply and to present their claims more robustly. The examining process serves as an important oversight mechanism that increases the transparency and accountability of the expert institution, thereby encouraging Experts to prepare more diligent and impartial reports.
However, the implementation of the examining procedure may also bring some practical problems such as cost, time, and impartiality. The solution to these problems lies in the proactive and effective case management to be demonstrated by the arbitral tribunal. Clearly defining the procedural rules at the beginning of the process, encouraging modern and efficient examining methods, and maintaining control at every stage of the proceedings will minimize these potential problems. In conclusion, when properly structured and effectively managed, the examining of the Expert is a fundamental procedural tool that enhances the fairness, legitimacy, and reliability of international arbitration.
B. KEY TAKEAWAYS
(1)Major arbitral rules (ICC, LCIA, UNCITRAL, ISTAC, ITOTAM) and the IBA Rules recognize the right of parties to question the Expert as a fundamental procedural safeguard.
(2)This right is essential to the principles of fair trial, adversarial proceedings, and equality of arms, allowing the parties to test the reliability of the expert report.
(3)The IBA Rules uniquely allow Party-Appointed Experts to question the Expert directly, enabling expert-to-expert technical discussion.
(4)Modern, collaborative methods such as hot-tubbing are increasingly preferred alongside traditional cross-examination.
(5)Parties often engage shadow experts to analyze the report and assist in preparing for examination.
(6)The existence of this right enhances transparency and accountability, incentivizing experts to prepare more careful and impartial reports.
(7)Practical challenges—cost, time management, impartiality concerns, and differing legal cultures—can be resolved through effective case management.
(8)The tribunal must establish the rules governing expert examination at an early stage to ensure predictability and fairness.
(9)Expert examination assists the tribunal in understanding technical matters more deeply, contributing to a more accurate and fair award.
(10)Allowing Party-Appointed Experts to question the Expert increases the reliability and legitimacy of the process in resolving technical disputes.
