Quantum of Damages in International Arbitration: A Solicitor's Guide
Damages quantification in international arbitration follows the substantive law governing the dispute - which may be English contract law, civil law principles, or international investment law. The quantum expert must adapt methodology to the applicable standard of reparation while meeting the procedural requirements of the arbitral institution.
This guide covers the IBA Rules on Evidence approach to experts, witness conferencing (hot-tubbing), the Chorzów Factory full reparation standard, and practical differences between ICC, LCIA, and ICSID proceedings.
IBA Rules on Evidence: Party and Tribunal Experts
Article 5 of the IBA Rules on the Taking of Evidence in International Arbitration (2020) governs party-appointed experts. Each party submits an expert report with the expert's qualifications, instructions, methodology, and conclusions. Article 6 allows the tribunal to appoint its own expert, whose findings are subject to party comment. Experts must be independent and owe their primary duty to the tribunal. Reports should follow the IBA structure: scope of assignment, factual assumptions, methodology, results, and sensitivity analysis. Tribunals in ICC, LCIA, and ICSID cases routinely expect party experts to meet before the hearing and produce a joint document identifying agreements and disagreements.
Hot-Tubbing and Witness Conferencing
Witness conferencing - commonly called hot-tubbing - involves opposing experts giving evidence concurrently before the tribunal, enabling direct dialogue and real-time clarification. The tribunal may direct the sequence of questioning, put its own questions, and ask experts to respond to each other's assumptions. This procedure is standard in investment treaty and complex commercial arbitration. Experts must defend their models under immediate scrutiny - unsupported DCF assumptions or cherry-picked comparables are exposed quickly. Solicitors should prepare experts for conferencing by reviewing the opposing report in detail and agreeing a list of methodological disputes in advance.
The Chorzów Factory Full Reparation Standard
In investment treaty arbitration, the applicable standard is full reparation under customary international law, as articulated in Factory at Chorzów (1928): the respondent must wipe out all consequences of the illegal act and restore the claimant to the position it would have been in had the act not occurred. For direct expropriation, fair market value at the date of expropriation is the primary measure. For indirect expropriation and fair and equitable treatment breaches, tribunals apply DCF or lost profits methodology depending on the investment's characteristics. The expert must identify the applicable standard in the report introduction and align methodology accordingly - English contract law but-for analysis alone is insufficient in ICSID proceedings.
DCF Methodology in Arbitration
Discounted cash flow analysis is the most common method for quantifying investment treaty and commercial arbitration damages where the business had an operating history and reliable projections. The expert constructs free cash flow projections, applies a discount rate (WACC), and calculates terminal value. Tribunals scrutinise growth rates, margin assumptions, and terminal value methodology heavily - sensitivity tables showing outcomes at alternative assumptions are essential. DCF is inappropriate for start-ups without track record or where cash flows are too speculative; market-based approaches (comparable transactions, stock market multiples) may be preferred. The expert should explain why the chosen method is appropriate for the specific investment.
ICC, LCIA, and ICSID: Procedural Differences
ICC arbitration under the ICC Rules typically involves terms of reference, a procedural timetable for expert reports, and a hearing with witness conferencing at the tribunal's discretion. LCIA arbitration under the LCIA Rules follows similar principles with emphasis on efficient case management. ICSID proceedings (Convention and Additional Facility) have specific requirements for expert evidence in annulment and enforcement contexts, and investment treaty claims often involve state respondents with sovereign defences affecting quantum. UNCITRAL ad hoc rules apply in many bilateral treaty cases. Regardless of institution, instruct counsel to confirm the applicable substantive law on damages early - the quantum expert's methodology must follow that law, not assume English law by default.
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