DETERMINATION OF THE EXPERT WITNESS IN ARBITRATION: THE LEGAL NATURE OF THE PARTY AGREEMENT AND THE JURISDICTION OF THE ARBITRAL TRIBUNAL

I. INTRODUCTION

In arbitration proceedings, party autonomy is one of the determining factors shaping the dispute resolution process. Unlike judicial courts, arbitration is based on the principle of party autonomy; the parties can largely determine the method of resolving their disputes, the arbitrators, and the procedural rules to be applied1.

The parties being able to determine the procedural rules applicable to the resolution of the dispute enables the process to proceed in a flexible, fast, and practical manner. Pursuant to Article 424 of the Code of Civil Procedure No. 6100 (“CCP”)2, the parties may freely agree among themselves on the rules relating to the arbitral proceedings, provided that mandatory rules are preserved3. As a natural consequence of this, party autonomy also plays an important role in the collection and evaluation of evidence in arbitration. Especially in disputes whose resolution requires technical or specialized knowledge, expert examination can be decisive in the proof of claims and defenses. At this point, it is important to establish a balance between the agreements made by the parties in regard to the determination of experts and the authority of the arbitrators to appoint experts.

The role of experts in arbitration and the methods by which they are determined either by the parties or by the arbitrators are addressed in detail in national legal systems, institutional arbitration rules, and non-institutional international instruments. On the one hand, national legislation, namely the International Arbitration Act No. 4686 (“IAA”)4 (Article 12) and the CCP (Article 431), expressly provides that experts may be resorted to in arbitral proceedings. Similarly, the Swiss Private International Law Act (Article 184) recognizes the arbitrators’ authority to appoint experts and request reports, while also allowing the parties to submit expert opinions. In England, the Arbitration Act 1996 (Article 37) grants the arbitral tribunal, unless otherwise agreed by the parties, an explicit statutory power to appoint experts, request information and documents, and order expert examinations.

On the other hand, the arbitration rules of leading institutions such as the International Chamber of Commerce (“ICC”)5, the London Court of International Arbitration (“LCIA”)6, the Istanbul Arbitration Centre (“ISTAC”)7 as well as the arbitration rules of the United Nations Commission on International Trade Law (“UNCITRAL”)8 which are frequently taken as a basis in ad hoc arbitration, also regulate the authority of arbitrators to appoint experts and the conditions of such authority.

The legal nature of party agreements in regard to procedure or evidence in arbitration, and the limits of such agreements, are discussed in light of mandatory legal rules and public policy. Although the parties may adapt the arbitral procedure to their own will by making agreements concerning the conduct of the process, conflicts that may arise in the course of the arbitrators’ application of these agreements may become critical at the stages of enforcement or annulment of arbitral awards. This matter is expressly regulated in Turkish arbitration legislation. In fact the CCP (Article 439/2-e) and the IAA No. 4686 (Article 15/A/1-f) provide that, if the arbitral proceedings are conducted in violation of the party agreements in regard to procedure, this shall constitute a ground for annulment. Similarly, the New York Convention9 recognizes the case where the arbitral procedure is not in accordance with the agreement of the parties as an obstacle to the enforcement of an arbitral award10. In this context, the failure of arbitrators to comply with a procedural rule agreed upon by the parties in regard to experts may constitute a procedural irregularity and jeopardize the validity of the arbitral award. Therefore, where the parties have agreed upon a procedure in regard to experts, it is of great importance that the arbitrators adhere to this agreement.

II. THE EXPERT IN ARBITRATION

A. The Role and Importance of Experts in Arbitral Proceedings

In arbitral proceedings, the expert is a specialist consulted in matters requiring technical knowledge and expertise concerning the subject of the dispute that the arbitrators are tasked to resolve11. As in state adjudication, the opinion of the expert in arbitration is a form of evidence that is not binding and may be freely assessed; although it is not absolutely binding on the decisions of the arbitrators, in many cases it can be decisive for the resolution of the dispute.

The existence of experts is closely related to the right to be heard in arbitral proceedings12. A party’s request for an expert examination on a technical matter is significant for the proper consideration of that party’s claims and defenses. An arbitrators’ rejection of such a request without any justification, particularly where the resolution of the dispute depends on technical data, may violate that party’s right to be heard and right to present evidence. In this regard, arbitrators must also ensure equal treatment of the parties with respect to their opportunity to present evidence. The principle of equality of the parties does not merely signify mathematical equality; rather, it entails granting the parties the opportunity to present the necessary evidence to support their claims and defenses. What matters is that the evidence presented by a party is taken into account by the arbitrators, thereby providing the parties with the possibility to have an influence on the final award13. If one of the parties alleges that the report prepared by its appointed expert has been disregarded by the arbitrators, this may form the basis of a claim that it was deprived of an equal opportunity to exert influence. Therefore, it is imperative for arbitrators, when assessing requests for expert examinations and expert reports, to observe the principles of equality of the parties and the right to be heard14.

On the other hand, the use of expert evidence may prolong the proceedings and generate additional costs. Therefore, arbitrators should not automatically appoint an expert upon every request but should first assess, in light of the existing evidence, whether the dispute can be sufficiently clarified without such recourse. Inefficient use of expert evidence may lead to both a loss of time and an increase in costs during the process. In fact, the ICC’s 2018 report entitled “Techniques for Controlling Time and Costs in Arbitration”15, stated that the costs associated with parties’ procedural submissions constitute the largest portion of the total costs, and that a significant part of these costs arises from the unnecessary submission of witness and expert evidence.

Conversely, if the opinion of an expert is indispensable for resolving a technical matter, it cannot be deemed reasonable for the arbitrators to refrain from considering the request for an expert. For the ultimate purpose of the arbitral process is to render a fair and enforceable award in accordance with party autonomy, and it cannot be overlooked that expert reports, in many cases, play a decisive role in achieving this purpose.

B. Appointment of Experts in Arbitration

In arbitral proceedings, there are multiple methods of resorting to expert evidence, and in this respect the parties’ autonomy and the authority of the arbitral tribunal have been arranged in a balanced manner. In general, two different practices have developed: experts appointed by the parties (party-appointed experts, private experts, or expert witnesses) and experts appointed by the arbitrators (independent experts). In international arbitration practice, under the influence of the Anglo-American procedural tradition, it is quite common for each party to submit the opinion of its chosen expert in the form of a report, whereas in practices influenced by Continental European tradition, the method adopted is the appointment of an independent expert by the arbitral tribunal when deemed necessary16. According to the 2012 International Arbitration Survey of Queen Mary University, titled “Current and Preferred Practices in the Arbitral Process” in 90% of arbitral proceedings experts are appointed by the parties, while only 10% are appointed by the arbitral tribunal. Furthermore, while party-appointed experts are more common in Anglo-American practice (77%), tribunal appointments are more prevalent in Continental European practice (57%)17.

Today, arbitral proceedings envisage the use of both methods by establishing a balance between party autonomy and the discretionary authority of arbitrators. The parties may appoint their own experts to clarify the technical aspects of the dispute; conversely, the arbitral tribunal, when deemed necessary, may appoint a neutral expert with specialized knowledge on the subject matter of the dispute and obtain his or her opinion. This flexible approach serves to ensure that the use of experts in arbitration takes place in a swift, efficient, and fair manner.

In Turkish law, the provisions on the appointment of experts in arbitration recognize both elements of this dual model, originating from the parties and from the arbitrators. Article 12 of the IAA and Article 431 of CCP regulate in parallel the provisions on the appointment of experts in arbitral proceedings. Pursuant to both regulations, the arbitrator or the arbitral tribunal may appoint one or more experts to deliver a report on the matters determined. In addition, the arbitrators may decide that the parties provide the necessary explanations to the expert, submit the relevant information and documents, and conduct an inspection if deemed necessary.

In addition, the legislator has not confined itself solely to provisions concerning experts appointed by arbitrators but has also guaranteed the parties’ ability to present their own experts18. Indeed, both provisions stipulate that, after the expert report has been obtained, the experts shall (unless otherwise agreed) attend the hearing upon the request of one of the parties or if deemed necessary by the arbitral tribunal. At this hearing, the parties are granted not only the opportunity to directly question the appointed expert but also the explicit right to present and have heard their privately chosen experts.

These provisions secure, in Turkish arbitration law, both the authority of arbitrators to appoint independent experts on technical matters and, at the same time, the parties’ right to submit their own expert opinions. Accordingly, this framework in Turkish law demonstrates that the two fundamental methods of resorting to experts in arbitration may coexist.

Similarly, in international and institutional arbitration rules, a balance is struck between the authority of the arbitral tribunal to appoint experts and the parties’ right to present their own chosen experts. For instance, under Article 29(1) of the UNCITRAL Arbitration Rules, the arbitral tribunal, after consulting the parties, may appoint one or more independent experts to prepare a report on specific issues, while Article 29(5) provides that the parties may present their own expert witnesses to testify on matters in dispute. Likewise, leading institutional frameworks such as the ICC Arbitration Rules and the LCIA Arbitration Rules stipulate that arbitrators, where they consider it necessary, may appoint experts after consulting the parties, and that the parties may present their own expert witnesses. In addition, Article 29(3) of the ISTAC Arbitration Rules provides that the arbitral tribunal may hear the experts appointed by the parties and, if it deems necessary, may appoint an expert after consulting the parties and defining the scope of the task. These rules set out the procedure by which arbitrators may appoint a neutral expert when expert opinion is required, while at the same time not restricting the parties’ right to present their own experts.

In conclusion, in international arbitration practice, the use of both party-appointed experts and tribunal-appointed experts has become a general principle. Depending on the nature of the dispute, the parties may bring their own experts to technically support their positions, while the arbitral tribunal, when necessary, may ground its decision on a scientific basis through the examination of a neutral expert.

Non-binding legal instruments concerning this dual approach also provide significant guidance in practice. In particular, the International Bar Association’s (“IBA”) 2020 revised Rules on the Taking of Evidence in International Arbitration (the “IBA Rules”) expressly set out the distinction between party-appointed and tribunal-appointed experts. Article 5 of the IBA Rules regulates the procedure concerning expert witnesses submitted by the parties, while Article 6 establishes the principles applicable to experts appointed by the arbitral tribunal.

All these national and international regulations, together with guiding principles, set out the general framework for the determination of experts in arbitration; they define the foundations of a transparent and reviewable expert practice in which methods based on party autonomy and those based on arbitral discretion are employed together. Within this framework, the following sections will address the details of the parties’ appointment of their own experts, the authority of arbitrators to appoint experts, and the importance of independence in both scenarios.

1. Party-Appointed Experts

In international arbitration practice, it is a common practice for the parties to submit their chosen expert witnesses together with the expert reports prepared by them. Influenced by the Anglo-American procedural tradition, party-appointed experts are accepted as evidence in arbitral proceedings19.

Although party-appointed expert reports are submitted at the request of one party, they essentially serve an evidentiary function in order to clarify a technical issue in the proceedings. The arbitral tribunal freely evaluates the opinions and reports submitted by party-appointed experts together with other evidence; the admissibility and probative value of such evidence lies within the discretion of the arbitrators20.

In practice, although each party tends to select an expert who will provide an opinion favorable to its position, experts are nevertheless expected to present their objective and professional assessments. Indeed, pursuant to Article 5 of the IBA Rules, a party-appointed expert report must include not only a disclosure of the relationships between the expert and the parties (or their counsel) but also a statement regarding the independence of the expert. This provision emphasizes that even a party-appointed expert is required to act as objectively and independently as possible when presenting an opinion.

2. Tribunal-Appointed Experts

Under the influence of the Continental European tradition, arbitration has adopted the possibility for arbitrators to appoint an independent expert when necessary21. Numerous institutional rules and national legislations confer authority on arbitrators to appoint experts. For instance, Article 29(1) of the UNCITRAL Arbitration Rules provides that the arbitral tribunal, after consulting the parties, may appoint one or more independent experts.

Similarly, Article 25(3) of the ICC Rules and Article 29(3) of the ISTAC Rules expressly provide that arbitrators may appoint experts where they consider it appropriate. Experts appointed by the arbitral tribunal, similar to those appointed by state courts, must be independent of the parties to the dispute and provide their expert opinion impartially. The general understanding in arbitration practice is that tribunal-appointed experts, like arbitrators themselves, are subject to standards of impartiality and independence.

Indeed, pursuant to Article 6 of the IBA Rules, an expert appointed by the arbitral tribunal must submit a declaration of independence before delivering a written report, and the parties may raise objections to the expert’s qualifications or impartiality within a specified period. Tribunal-appointed experts are generally tasked with assessing the technical dispute in the file from a neutral perspective; in this way, if the parties have submitted conflicting expert opinions, the arbitral tribunal is able to weigh them more effectively. Nevertheless, the appointment of experts by arbitrators remains a relatively exceptional course of action.

In practice, arbitrators generally do not consider it necessary to appoint their own expert where the parties have already submitted experts22; however, if the technical contradiction between the parties’ statements is so profound that it cannot be resolved, or if no party has submitted any expert, they resort to this course of action.

3. The Importance of the Independence and Impartiality of Experts

Regardless of the method, the proper functioning of the expert mechanism in arbitration critically depends on the independence and impartiality of the experts. Even experts appointed by the parties are expected to act objectively and in accordance with professional ethical standards. In this respect, various soft law instruments have been developed in international arbitration with the aim of enhancing awareness on this issue.

In particular, the “Protocol for the Use of Party-Appointed Expert Witnesses in International Arbitration”23 published by the Chartered Institute of Arbitrators explicitly defines the role of a party-appointed expert as assisting the arbitral tribunal and emphasizes that, regardless of which party bears the cost, the expert opinion must be independent, objective, and truthful. The Protocol also requires the expert to disclose his or her relationships with the parties, counsel, and the arbitral tribunal, thereby linking the principle of independence to a concrete procedure.

In parallel, the “IBA Guidelines on Party Representation in International Arbitration”24 impose ethical responsibilities not only on the expert but also on the counsel who directs the expert. These guidelines prohibit counsel from improperly interfering with the content of the expert report, encouraging false statements, or engaging in practices that undermine independence, thereby securing the integrity of the expert opinion through a dual safeguard.

Furthermore, pursuant to Article 5(2) of the IBA Rules, one of the elements required to be included in a party-appointed expert report is a disclosure of the expert’s relationships with the parties, their counsel, and the arbitral tribunal, together with a declaration of independence. Thus, the expectation from a party-appointed expert is to express the truths within his or her field of expertise. For tribunal-appointed experts, however, both the rules and practice impose a much stricter standard of impartiality. Article 29(2) of the UNCITRAL Rules provides that an expert appointed by the tribunal shall, before accepting the assignment, submit a statement regarding his or her qualifications. Likewise, Article 6(2) of the IBA Rules requires a tribunal-appointed expert to submit a declaration of independence and grants the parties the right to challenge this declaration.

As a result, whether appointed by the parties or by the arbitrators, the credibility of an expert is only possible to the extent of his or her independence and integrity. An expert who submits a heavily biased report on behalf of one party will face a credibility problem before the arbitrators; whereas any doubt cast upon the impartiality of an expert appointed by the tribunal will harm the proceedings as a whole and bring with it the potential risk of annulment of the arbitral award.

III. Party Agreement on the DETERMıNATıON of Experts and Its Legal Nature

In arbitral proceedings, the parties possess autonomy of will in resolving their private law dispute through arbitrators. Accordingly, for the resolution of the dispute, they may transfer the adjudicatory authority of the state to an arbitral tribunal of their own choosing. Both in national and international arbitration law, arbitral proceedings are essentially based on the free will of the parties.

Within this framework, the parties may freely determine the arbitrators who will resolve the dispute, the number of arbitrators, the procedure for their selection, the content of the arbitration agreement, the seat of arbitration, the law applicable to the merits of the dispute, the law applicable to the arbitral procedure, and the means of evidence to be relied upon. This possibility is referred to in arbitration law as the principle of “party autonomy”25.

Party autonomy is particularly manifested in the determination of the rules applicable to the arbitral procedure. Pursuant to Article 424 of the CCP, the parties may freely agree on the procedural rules to be applied by the arbitrator or the arbitral tribunal, provided that the mandatory provisions of this section are reserved, or they may determine them by reference to a law or to institutional arbitration rules. In the same vein, Article 8/A of the IAA provides that the parties may determine the procedural rules, again subject to mandatory provisions. This freedom enables the parties, in their arbitration agreement or clause, to regulate numerous procedural matters such as service of notices, conduct of hearings, burden of proof, and methods of submitting evidence.

The parties’ authority to regulate procedural matters is limited solely to the procedural rules to be applied by the arbitrators. In areas such as mandatory rules or matters of public policy, including provisions on legal remedies available against an award, the parties do not have such freedom. The parties may determine the procedural rules of arbitration either in the arbitration agreement or clause, or they may reach an agreement on this matter after the proceedings have commenced. However, agreements made during the proceedings do not have retroactive effect; they are applicable only prospectively26.

Instead of determining the rules applicable to the arbitral procedure one by one, the parties may also refer to the arbitration provisions of national legal systems or to international or institutional arbitration rules27. For instance, the ICC Rules, the ISTAC Rules, and the UNCITRAL Model Law are systems that give priority to party autonomy while leaving discretion to the arbitral tribunal only in matters not expressly regulated. Article 19 of the UNCITRAL Model Law provides that the parties are free to agree on the procedure to be followed by the arbitral tribunal in conducting the proceedings, and that, failing such agreement, the arbitral tribunal may conduct the arbitration in such manner as it considers appropriate, subject to the provisions of this Law. A similar approach is adopted in institutional arbitration rules. For example, pursuant to Article 19 of the ICC Rules, the proceedings shall be conducted, in the first place, in accordance with the ICC Rules; in the absence of a provision, in accordance with the procedure agreed upon by the parties; and in the absence of such agreement, in accordance with the procedure determined by the arbitral tribunal.

As a result, the procedural freedom granted to the parties in arbitration will encompass not only the general framework of the proceedings but also the use of evidence, including the determination of experts as a part thereof28. The parties may, through a procedural agreement contained in the arbitration agreement or concluded during the proceedings, determine whether an expert will be consulted, who will be appointed as the expert, and the method, duration, and scope of the preparation of the report. However, this freedom is not absolute; arrangements that contravene public policy, mandatory provisions, or the principle of equality of the parties shall be invalid. The independence and impartiality of the chosen expert must also be safeguarded; otherwise, the arbitral tribunal may, notwithstanding the party agreement, appoint an expert it deems appropriate.

Thus, party autonomy, while granting the parties a broad margin of discretion in the determination of experts, is balanced by the requirements of the right to a fair trial and the proper conduct of the proceedings.

IV. The JURISDICTION of the Arbıtral Trıbunal VIS-À-VIS Party Agreements

The arrangements made by the parties concerning expert evidence within the framework of party autonomy constitute a procedural agreement that directly affects the course of the arbitral proceedings and, as a rule, binds the arbitral tribunal29. In this context, the primary duty of the arbitral tribunal is to comply with the reasonable and practicable procedural choices of the parties, provided that they are not contrary to public policy or mandatory provisions. For an arbitrary or unjustified deviation from this procedural framework agreed upon by the parties would not only undermine the principle of predictability of arbitration for the parties, but also create a serious risk that the award rendered at the end of the proceedings may be subject to annulment or refusal of enforcement.

However, the procedural agreements made by the parties do not entirely eliminate the discretion of the arbitral tribunal30. The emergence of unforeseen circumstances during the course of the dispute, or the agreement of the parties becoming incomplete, ambiguous, or inapplicable, may necessitate the intervention of the arbitrators in order to conduct the proceedings properly and to ascertain the material truth. For instance, the parties may initially have agreed upon a single joint expert; however, if serious doubts arise during the proceedings as to the sufficiency or impartiality of the report, the arbitral tribunal cannot render its decision solely on the basis of that report.

In such circumstances, the arbitrators should first consult with the parties to encourage the development of a new agreement and, where possible, continue the process in a fair manner through the appointment of an additional expert or the supplementation of the existing report. The line between absolute adherence to party autonomy and the arbitrators’ duty to ensure a fair trial must, in such cases, be preserved through a flexible and cooperative approach.

When the arbitral tribunal is compelled to appoint an expert notwithstanding the parties’ agreement, it must afford the parties equal participation and the opportunity to present their views at every stage of the process. At phases such as the determination of candidate experts, the formulation of the terms of reference, the examination of the report, and the questioning of the expert, the active involvement of the parties is essential for the protection of both the principle of equality and the right to be heard31. The mandatory fundamental principles of arbitration, namely party equality and adversarial proceedings, cannot be set aside by any procedural agreement made by the parties. Therefore, even if the parties agree that no expert examination shall be conducted in a technically complex dispute, the arbitral tribunal, if it harbors serious doubts about the correctness of the decision, should invite the parties to reconsider their agreement; otherwise, it must take into account that the award may be exposed to claims of violation of public policy or of the right to a fair trial32.

In summary, although the jurisdiction of the arbitral tribunal is circumscribed by party agreements, these boundaries are not absolute in the face of public policy, equality, the principle of good faith, and the principles of a fair trial.

Arbitrators, by relying on the reasonable expectations of the parties, ensure the predictability and reliability of the arbitral proceedings; whereas the parties must refrain from rigid provisions that would hinder the tribunal from conducting the process properly. A balanced relationship established between party autonomy and arbitral discretion enables the effective use of expert evidence, thereby safeguarding both the accuracy and the enforceability of the award. Preserving this balance is the key to reaching outcomes that are fair, practicable, and acceptable to the parties, even in technically complex disputes.

V. CONCLUSION

The determination of experts in arbitration proceedings is a process that reflects the delicate balance between party autonomy and the authority of the arbitral tribunal. Whether the parties present experts of their own choosing, agree on a joint expert, or leave the matter entirely to the tribunal, the ultimate goal in every case is to achieve a fair, impartial, and accurate outcome. The legal character of party determinations holds great value in that it provides flexibility and predictability in arbitration. The arbitral tribunal, in turn, is obliged to conduct the proceedings fairly by respecting the reasonable expectations of the parties. Nevertheless, the arbitral process is not a unilateral mechanism under the exclusive control of either the parties or the arbitrators, but rather rests on cooperation and mutual trust .

The approach adopted by modern arbitration rules regarding experts fosters such cooperation: while parties are granted the opportunity to appoint their own experts, tribunals are likewise empowered to resort to independent expertise whenever they deem it necessary. Every step that accelerates or facilitates the resolution of the dispute is taken with the approval of the parties and under the guidance of the arbitrators. The validity of procedural agreements concluded by the parties is safeguarded within the framework of public policy and mandatory law; the arbitral tribunal is expected to act in accordance with these agreements. Otherwise, difficulties may arise at the enforcement stage of the award. Indeed, from the New York Convention to domestic statutes, numerous instruments consider adherence to party autonomy as a measure of the legitimacy of arbitration proceedings.

In conclusion, the issue of the determination of experts in arbitration reminds us of two fundamental values at the core of arbitration: autonomy and justice. By virtue of their autonomy, the parties enjoy the freedom to shape the proceedings according to their own needs. The arbitral tribunal, in turn, holds the authority to employ the necessary tools in order to conduct a fair trial and to reach the material truth. When party agreements and arbitral authority concerning expert evidence are properly harmonized, it becomes possible to render accurate awards that are accepted by all parties, even in technically complex disputes. Arbitration conducted with due regard to this balance not only ensures respect for party autonomy but also guarantees that awards will be reliably enforced before national and international enforcement authorities. It is evident that, in the future of arbitral proceedings, the institution of experts will continue to evolve in light of these principles and will keep providing flexible solutions responsive to the needs of the parties.