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This article has been written by Shubham Sharma, pursuing a Diploma in Advanced Contract Drafting, Negotiation and Dispute Resolution from LawSikho.


Arbitration has two hard realities. Firstly, it often involves complex issues: disputes arising out of infrastructure projects, advanced technology or maritime trade can involve questions of such nuance that may only be answered reliably by the experts in those respective areas. In such situations, arbitral tribunals appoint experts who tender their opinion as evidence to assist the tribunal in reaching a conclusion. Secondly, it is expensive: where the parties have to bear the cost of the arbitrators, the counsels, the institution and the various process fees involved, each day spent in arbitration burns a deep hole into the parties’ pockets. 

In such arbitrations, a substantial time and effort goes into examining expert evidence. In the face of this problem, ‘Hot-Tubbing’, or less interestingly, witness conferencing is an emerging solution that is rapidly being accepted internationally. This article expands upon this concept and analyses how far India has come to adopt it.

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What is Hot-Tubbing?

In the words of Hon Justice McClellan, Chief Judge at Common Law of the Supreme Court of New South Wales, Hot-tubbing is- 

“a discussion chaired by the judge in which the various experts, the parties, the advocates and the judge engage in a co-operative endeavour to identify the issues and arrive where possible at a common resolution of them.” 

Hot-tubbing or witness conferencing is one of the leading techniques for admitting evidence in international arbitration. In this approach, expert witnesses are sworn together and asked to tender their opinion concurrently and in confrontation with each other without the constraints of an adversarial process. The tribunal under this process is allowed to ask questions directly to each witness and start a structured discussion to arrive at the best conclusion available. Counsels of the parties are allowed to examine and cross-examine the witnesses once the tribunal has elicited the evidence. Hot-tubbing differs from the traditional method of leading evidence wherein each party leads the case wholly and sequentially with witnesses and expert witnesses who will be first examined and then cross-examined separately.

As is evident from the process itself, this method of leading evidence is more in the tune of a dialogue rather than a verbal battle between the witness and the counsels. The tribunal dons the hat of the leader of the discussion and the counsels’ participation is restricted to stating the objections. This approach allows the tribunal to reach the root of the issue more constructively and with much less time and efforts.

Notably, hot-tubbing is not provided mandatorily under the rules of any of the international arbitration institutions. The International Bar Association (IBA) however, under its ‘Rules on Taking of Evidence in an International Arbitration’, gives legislative recognition to hot-tubbing under Article 8(4)(f) which states- “the Arbitral Tribunal, upon request of a Party or on its own motion, may vary this order of proceeding, including the arrangement of testimony by particular issues or in such a manner that witnesses be questioned at the same time and in confrontation with each other (witness conferencing)”

What are the aims of hot-tubbing?

The aims of hot-tubbing as delineated by Gilbert Samber, a US Attorney, are:

  1. To promote objective impartiality, and to reduce or eliminate bias or advocacy, in expert evidence;
  2. To ensure that experts answer the same questions, based on the same assumptions, at about the same time;
  3. To improve the responsiveness, precision and clarity of expert evidence.

Advantages of hot-tubbing

Quick and less expensive

As opposed to the traditional method of seeking expert evidence which can sometimes take weeks, the process of hot-tubbing can be concluded, in most cases, in a day or two. With respect to arbitration, where a single session costs enormously to the parties, this method can substantially reduce the cost of the arbitration.


Experts’ testimony in hot-tubbing is concurrent. The reduced time lag between the testimonies results in greater understanding. It also allows the tribunal to identify and address any fallacies in the testimonies at the earliest instance. 

Better assessment of the credibility of each witness

Under hot-tubbing, the tribunal is not expected to be a silent spectator. The response of the experts to the questions or concerns posed by the tribunal makes for an easy assessment of the experts’ credibility. Particularly when the experts are also allowed to respond to each others’ testimony and raise questions. 

Increased opportunity for the testimony to provide needed information to the tribunal

The more fulsome exploration of issues and questions provided by concurrent testimony are likely to improve the quality and amount of needed information available to the tribunal.

Expert Witness in India

Under the Indian Evidence Act, 1872, (hereinafter: “IEA”) a distinction is drawn between an expert and a non-expert witness. The testimony of a non-expert witness is receivable under Section 9 of the IEA which can pertain to questions such as the identity, conditions, age, appearance or resemblance of things. However, in questions that require a certain expertise, it is best to seek the opinion of a person who has adequate knowledge in that specific field.

Expert witnesses are recognized in India under Section 45 of the IEA. The section stipulates that when the court has to form an opinion upon a point of foreign law, science, art, or identity of handwriting, opinions of persons specifically skilled in those respects are relevant facts. Such specifically skilled persons are regarded as experts. It is trite law that although an expert’s opinion is valuable to the case, it cannot be read as conclusive and has to be tried by the court. Hence, an expert’s opinion as well as his credibility can be cross-examined.

Hot-Tubbing in India

The process of hot-tubbing is not alien to the Indian legal regime. Under the amended Delhi High Court (Original Side) Rules, 2018, Section 6 under Chapter XI gives recognition to hot-tubbing in commercial disputes. The section states that the court may, by its own accord or by an application by the parties, permit expert testimony by way of hot-tubbing. The section places a robust mechanism under Annexure G and also grants liberty to the court to mould the process according to the requirements of the case. 

The Delhi High Court, in Micromax Informatics Ltd. vs Telefonaktiebolget Lm Ericsson, the court categorically discussed the nature and scope of hot-tubbing. The facts involved a patent dispute wherein the parties showed their desirability to adopt hot-tubbing. The court held “With respect to the procedure that can be used to arrive at a swifter resolution of disputes (such as in patent cases, involving technology and scientific experts‟ testimony and evidence), this court is of the opinion that patent disputes and those that involve examination of expert evidence should adopt the hot-tubbing procedure.” 

However, the court also expressed its concerns over the importance of judicial intervention for the success of the process. The court observed that the judiciary in India is already under great time pressure, if hot-tubbing is to be used more widely, judges would require preparatory time and special training to undertake this role. 


With respect to Arbitration in India, the Arbitration and Conciliation Act, 1996 does not have any provision that directly deals with hot-tubbing or concurrent expert evidence. Yet, under section 19 of the A&C Act, the tribunal is not bound by the procedural or evidentiary law of the country and the parties are free to agree on the procedure to be followed by the arbitral tribunal. Hence in arbitration, the arbitral tribunal and the parties are free to opt for hot-tubbing as their method for taking expert evidence.

The process of hot-tubbing is undoubtedly a more superior mechanism to elicit evidence than the traditional process. The recognition it has been given by the Delhi High Court goes to show that we may witness the Indian legal regime shifting towards a lesser combative model in the near future. 

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