Practitioners who move from U.S. federal court litigation into international commercial arbitration often assume that witness testimony will work the way they know. It does not. The structural differences — how testimony is submitted, how cross-examination is conducted, how experts are presented — are substantial, and they affect both how cases are prepared and how hearings are run. Understanding those differences, and understanding the emerging Prague Rules alternative, is essential for anyone handling cross-border disputes involving U.S. and Latin American parties.
How Witness Testimony Differs from U.S. Litigation
Practitioners trained in U.S. litigation often enter international arbitration expecting a familiar testimony framework: witness stands, oath, direct examination by proponent's counsel, cross-examination by opposing counsel, redirect, recross. International arbitration typically works differently, and the differences matter tactically.
The most significant departure is the witness statement. In international arbitration, witnesses for each party ordinarily submit written witness statements in advance of the hearing — sometimes called witness statements, sometimes "written testimony." These statements stand in for direct examination. At the hearing, the witness's direct examination is typically limited to a brief confirmation of the statement (or the statement is simply admitted without live direct), and cross-examination follows. Some tribunals allow a brief live direct before cross; many do not.
This structure has significant implications. The witness statement must be persuasive, narrative, and structured — it is the primary vehicle for that witness's evidence. It must also survive cross-examination, which means it must be consistent with the documents in the record. A witness statement that overstates, omits inconsistent facts, or diverges from documentary evidence is dangerous precisely because the witness cannot use live direct examination to explain away the problem.
The IBA Rules on Evidence and Witness Testimony
Under the IBA Rules on Evidence (Article 4), witnesses of fact submit written statements well in advance of the hearing. The statements must: describe the witness's factual knowledge, identify the documents the witness is relying on, be signed by the witness, and confirm that the witness understands the obligation to tell the truth. Expert witnesses submit separate expert reports under Article 5.
At the hearing, the witness is cross-examined by opposing counsel and may be questioned by the tribunal. There is no formal redirect examination in the U.S. sense, though some tribunals allow brief clarifying re-examination. The tribunal controls the hearing and may ask questions of witnesses directly — often substantively important questions that neither party anticipated.
Article 4(8) of the IBA Rules allows a party to object to a witness appearing at the hearing. If the witness does not appear for cross-examination, the tribunal gives the witness statement whatever weight it considers appropriate — which in practice often means significantly reduced weight, sometimes near zero.
Cross-Examination in International Arbitration — More Constrained Than U.S. Practice
Cross-examination in international arbitration is typically more limited in scope and duration than in U.S. litigation. Tribunals actively manage hearing time — cross-examination allocations of one to four hours per witness are common even in complex matters, compared to the unlimited scope that U.S. trial lawyers expect.
The effective cross-examiner in international arbitration prioritizes ruthlessly: what are the two or three things this witness can confirm or admit that advance my case? A cross-examination that tries to cover everything — the U.S. trial approach — wastes limited time and risks rehabilitating the witness by giving them extended time on the stand. Tight, document-focused, closed cross-examination — confirming facts the witness cannot deny without damaging their credibility — is more effective in the international context.
Witness preparation in international arbitration must account for both the witness statement preparation phase (which is itself a significant exercise) and the cross-examination preparation. Witnesses who have never experienced the international arbitration hearing format need specific preparation for what to expect — the structure of the hearing, the role of the tribunal, the scope of cross-examination, and the limitation on live direct testimony.
Expert Witnesses — The Concurrent Expert Session ("Hot-Tubbing")
Expert witness procedures in international arbitration often depart even further from U.S. litigation norms. Concurrent expert testimony — often called "hot-tubbing" — has become increasingly common. In a hot-tub session, both parties' experts are seated together before the tribunal, questioned jointly (sometimes by the tribunal first, then by counsel), and invited to respond to each other's positions in real time.
The rationale for hot-tubbing is efficiency and quality of expert input: the experts can engage each other directly on their disagreements, the tribunal can probe the areas of genuine dispute without the filter of opposing counsel's questions, and the session is typically shorter than sequential expert examination. The IBA Rules do not require hot-tubbing, but tribunals may order it, and parties increasingly agree to it in procedural orders.
For U.S.-trained practitioners, hot-tubbing requires a different approach to expert preparation. The expert must be prepared to defend their position in a live, unscripted dialogue with the opposing expert — not just to deliver prepared answers to anticipated questions. Experts who are strong on paper but weak in spontaneous technical discussion perform poorly in hot-tub sessions.
The Prague Rules — An Alternative Approach
The IBA Rules on Evidence reflect the common law tradition — party-driven document production, witness statements, oral cross-examination. The Prague Rules (formally the Rules on the Efficient Conduct of Proceedings in International Arbitration), adopted in 2018, reflect a civil law approach that is increasingly common in disputes involving parties from civil law jurisdictions.
Under the Prague Rules, the tribunal plays a more active role: it may identify legal and factual issues early, request specific documents rather than allowing open-ended production, limit witness testimony to issues that are genuinely in dispute, and take a more inquisitorial approach to hearings. The Prague Rules de-emphasize oral cross-examination and encourage written submissions to resolve issues that do not require live testimony.
For LATAM-connected disputes, the Prague Rules are worth understanding. Many LATAM parties and their counsel come from civil law systems where the inquisitorial model is familiar. A tribunal that applies the Prague Rules by agreement of the parties may move more efficiently and produce fewer procedural objections from LATAM parties than a tribunal applying IBA rules whose cross-examination procedures feel adversarial and foreign.
The choice between the IBA Rules and the Prague Rules is not binary. Tribunals regularly combine elements of both, adopting Prague-style active case management while preserving cross-examination rights for witnesses whose testimony is genuinely contested. The key is building the procedural framework into the first procedural order, before either party has committed to a presentation strategy that assumes one approach or the other.