‘Hot-Tubbing in Arbitration’ – The Latest Fad or a Creative Solution Here to Stay?

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Arbitrations often involve dealing with questions pertaining to complex technical, financial and monetary, cultural, and linguistic issues. It may be impossible for the counsel and the arbitrators to know and understand these issues fully without any additional support or help from the experts in those particular fields. Thus, expert opinions, or rather the testimonies of the experts, play an important role in multi-faceted or complex arbitrations.

The role of the expert witness is not to assert the client’s position but to help assist the Tribunal in getting all the information to arrive at a decision regarding the issues central to the dispute. However, in practice the former objective is aimed to be fulfilled by the expert rather than the latter. Apart from the bias harboured by the expert towards its client, there are other lacunae with the expert testimonies such as information overload by the expert, inability of the other side’s counsel to properly examine the arbitrator, and most importantly conflict between the experts of both/all sides on pertinent issues. These problems regarding taking expert witnesses’ testimonies are not just faced in arbitration but also in other civil and criminal litigations. To resolve all the mentioned problems that arise with the expert testimonies, a unique process, ‘hot-tubbing’ was evolved.

Evolution of the concept and its procedural usage

‘Hot-tubbing’ is the procedure of presenting concurrent expert testimony, i.e. the experts brought forward by both/all sides to a dispute are made to concurrently give their testimonies in the form of a discourse between the experts, to bring out the truth in a more reliable and efficient manner. This unique process of the examination of the expert witnesses finds its origin in Australia but is now regularly adopted in international arbitrations. Recently, The Delhi High Court amended its Rules (Original Side) and incorporated ‘Hot-tubbing’ by substituting Rule 6 in Chapter XI of the Rules.[1]

Although the format of hot-tubbing differs from case to case, the essential point is that the experts are called in at the same time and the arbitrator chairs a discussion between them. The submitted documents for the matters upon which the experts agree/disagree serve as the agenda, and the Counsel is able to join in the discussion and can put questions to the experts. The key difference, and a way for identifying the truth behind the conflicting testimonies, is that the experts can pose questions to each other.

The International Chamber of Commerce (ICC) Commission Report on Controlling Time and Costs in Arbitration has also identified ‘witness conferencing’ as a technique that may be useful in suitable cases.[2] However, as there are two sides to every coin, the practice of hot-tubbing also has both advantages and disadvantages.


  • The experts may be more likely to make concessions and reach a greater degree of agreement by constructive discussions in the hot-tub, where they are relaxed, than through cross-examination.
  • The experts are often asked to answer questions at the same time which makes the hot-tubbing effective in identifying the areas where the experts agree or disagree.
  • Most of the times the questions are open ended, so as to elicit the responses on spot and in a manner conducive to the understanding of the Tribunal, and not leave much room for the experts to answer as trained parrots, as may happen in cross-examinations.
  • As each expert is subject to simultaneous peer scrutiny, the risk of the experts giving vague answers that favour the client is reduced, leading to lesser inaccuracies in the expert testimony.
  • It is a time and cost saving method as it eliminates the need of examination and cross-examination of experts separately.
  • The testimonies at the end of the hot-tub process are much more conclusive and reliable as they are the result of deliberation and discussion between the experts.
  • The fearsome combat-style cross-examination is eliminated, which may help the experts in giving a clear and concise testimony due to lack of fear of the cross-examination.
  • The experts may tend to simplify their information further for the benefit of the Tribunal by being part of the discussion which involves active participation of the arbitrators.


  • The Counsel (representing their clients) may lose control of their case as the questions by the other side are posed to the experts simultaneously and on spot, therefore not giving the experts enough time to prepare a testimony which would be beneficial to the client.
  • The Arbitrator(s) may not have an adequate grasp of the complex issues or subjects that the experts deal in to question the experts effectively and ascertain the veracity of the testimony.
  • The possibility of the experts digressing from the relevant points whilst in the process of a peer discussion cannot be overlooked.


The merits of this process of taking concurrent evidence have been considered by various jurisdictions, and have been incorporated in their legal systems, without being restrictive to arbitrations. The country from which we trace the humble beginnings of our present legal system, the UK, had also passed an amendment to the Practice Direction to CPR (Civil Procedure Rules) Part 35, way back in April 2013, to give the Courts “the power to order that experts give evidence concurrently”.[3]

Hot-tubbing’s formal acceptance in UK and now by Delhi High Court clearly signifies that the process has proved to be an effective solution for ensuring reliable expert testimonies and is not just a fad. However, using the process in the arbitrations is still a rarity and not a norm, as the principle of party autonomy is vital in determining the procedures of an arbitration. Moreover, as every new development takes time to be understood, accepted and used widely, the process of hot-tubbing too is yet to gain momentum as a standard industry practice in India.

This article has been contributed by Kushangi Sewani, a 5th year student of Symbiosis Law School, Pune. She has a keen interest in International Arbitration and Dispute Settlement. 


[1] Notification available at

[2] Report available at

[3] Available at

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