The legitimacy of arbitration depends heavily on confidence in the tribunal’s independence and impartiality. But when does an arbitrator’s prior encounter with a witness in an unrelated arbitration become sufficient to raise a concern about apparent bias? In O v S [2026] HKCFI 4910, the Hong Kong Court of First Instance considered an application to set aside a Partial Award arising from an HKIAC arbitration seated in Hong Kong.
The applicant alleged apparent bias by the presiding arbitrator, Member R, who had previously presided over an unrelated arbitration in which Witness Z, a factual witness in the present proceedings, had given evidence. The party relying on Witness Z had lost that arbitration, and Member R had not disclosed his prior involvement. Although Witness Z said he did not recognise Member R during the later arbitration, the Court considered that the close timing between the proceedings meant the previous encounter would likely have been remembered by Member R.
The Court applied the fair-minded and informed observer test: would such an observer conclude that there was a real possibility of bias? It stressed that prior exposure to a witness, or even a previous adverse view of that witness’s evidence, would not ordinarily suffice. There must be a logical connection between the circumstances and the possibility that the arbitrator could not approach the case impartially.
The position could differ where there was personal friendship or hostility, a close relationship, or extreme criticism of the witness’s honesty or integrity. While prior consideration of a witness’s evidence would not ordinarily require disclosure, exceptional circumstances may make disclosure necessary. Importantly, non-disclosure does not automatically establish apparent bias. It is simply one factor for the fair-minded and informed observer to consider.
Here, the Court placed weight on the Partial Award itself. Although Witness Z’s credibility had been challenged, the Tribunal made no adverse finding concerning his credibility or reliability. Its conclusions instead rested on documentary evidence and inherent probabilities. The Court therefore found no real possibility that Member R’s prior exposure to Witness Z had influenced the Tribunal.
The applicant’s inability to know what Member R remembered from the earlier arbitration was described as its “most attractive argument”. Nevertheless, the Court held that this amounted only to doubt or speculation, not a real possibility of bias. Even if apparent bias had been established, the applicant would still have had to demonstrate prejudice, which it failed to do.
The Court also rejected the bifurcation challenge, finding no breach of the parties’ agreement to divide the proceedings into liability and quantum phases. The Tribunal had acted within its case-management powers.
O v S hence reinforces that apparent bias cannot be established by suspicion alone. What matters is whether the circumstances, viewed objectively and in their entirety, create a real possibility that the arbitrator could not approach the dispute with an open mind.