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A "hot-tub" is a large tub filled with hot aerated water used for recreation or physical therapy.

“Hot-tubbing”, “concurrent expert evidence” or “witness conferencing” is a method of giving overt testimony, in which both witnesses of opinion (or fact) give evidence simultaneously and the judges of the court, or arbitral tribunal, chairs a discussion between them.

The expert witnesses are ‘sworn-in’ together and sit in front of the tribunal, which puts the same questions to each expert witness in turn, effectively acting as the “chair” of a debate between those experts to get to the truth.

One theory behind its use is that the expert witnesses are more likely to make concessions and reach a greater degree of agreement in the hot-tub than under traditional witness box based cross examinations. In the hot-tub, the expert witnesses are generally more relaxed and can therefore have a more constructive discussion. No alcohol is involved!

When to be used:

  • When there is a significant disagreement between the expert witnesses.

  • Where the tribunal needs to be educated about the intricacies of the underlying case.

Pros and Cons


  • Easy determination of crucial issues due to an open and frank discussion

  • No more unclear answers. The experts clarify and there is no lack of clarity

  • Time and cost efficient

  • More useful as the expert witness is more likely to assist the tribunal to resolve the disputes

  • Better understanding for the tribunal

  • Likely to bring forward a settlement as both parties understand more clearly the strengths and weaknesses of their case


  • A single expert is better able to manipulate a discussion

  • Less room for advocacy and persuasion.

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