On 11 February 2026, in Buried Hill v. Turkmenistan, the two remaining arbitrators, Mr Siqueiros and Mr Goldberg (the “Unchallenged Arbitrators”), accepted Buried Hill Serdar Limited’s (the “Claimant”) proposal to disqualify Professor Philippe Sands, KC, from the tribunal. Their decision was based on Articles 14(1), 57 and 58 of the Convention on the Settlement of Investment Disputes Between States and Nationals of Other States (the “ICSID Convention”) and Rule 23(1) of the 2022 ICSID Rules of Procedure for Arbitration Proceedings (the “ICSID Arbitration Rules”).[1]
The Decision addresses a recurring problem in international arbitration: whether the same arbitrator can serve in two separate cases involving different legal claims but many of the same facts, witnesses and documents, as well as the same underlying asset. The Unchallenged Arbitrators rejected the idea that parallel appointments are automatically disqualifying. What mattered was the unusually close overlap in witnesses, documents, the underlying asset and the order of the hearings, which they found created an evident risk of unconscious influence and an information imbalance within the ICSID tribunal.[2]
I. Facts
Buried Hill’s ICSID claim concerned its investment in the Serdar oil field, now known as the Dostluk field, in the Caspian Sea. It alleged that Turkmenistan breached its obligations under the Energy Charter Treaty (the “ECT”) by encouraging Buried Hill’s investment through governmental promises before abandoning those commitments and excluding Buried Hill from any future development of the field.[3]
Separately, the Claimant was also pursuing an ICC arbitration against State Concern Turkmennebit under a 2013 Production Sharing Agreement.[4]
The legal bases, instruments and applicable laws of the two cases differed: the ICC arbitration concerned alleged contractual breaches by Turkmennebit and breaches of the contractually chosen applicable laws, whereas the ICSID case concerned Turkmenistan’s alleged breaches of the ECT and international law, including alleged breaches of the Claimant’s “legitimate expectations” concerning the development of the Serdar field.[5]
The factual overlap was nevertheless substantial: Buried Hill was the claimant in both cases, and both concerned the Serdar field. Turkmennebit was also described in the Decision as an instrumentality of Turkmenistan that Turkmenistan had not denied.[6]
The witness overlap was also extensive. All three factual witnesses who had submitted statements in the ICC Arbitration were also expected to testify in the ICSID case. The authors of two of the three expert reports submitted in the ICC Arbitration were also expected to provide expert evidence in the ICSID Arbitration.[7]
Professor Sands was already serving in the ICC Arbitration case when Turkmenistan appointed him to the ICSID tribunal. The ICC hearing on jurisdiction and the merits was expected to take place first, so he would likely hear and assess the shared witnesses before they appeared before the ICSID tribunal.[8]
The Claimant argued that Professor Sands’ role in both proceedings created a risk of unconscious influence and gave him access to information that the other arbitrators could not assess.[9]
Turkmenistan opposed the Disqualification Proposal. It responded that the cases involved different respondents, legal instruments, applicable laws and causes of action. It also argued that any information gap could be addressed because Buried Hill was represented by the same counsel in both proceedings and the ICC record could be placed before the ICSID tribunal.[10]
Professor Sands did not believe that resignation was necessary. He explained that experienced arbitrators frequently encounter similar facts and legal questions and that he considered each case independently. He further observed that assessing a witness in one case does not predetermine how the same witness will be assessed on another issue.[11]
II. Issues
As a result, two questions arose: first, would the overlap create an “evident or obvious appearance” that impressions formed in the ICC case could unconsciously influence Professor Sands in the ICSID case?[12]
Second, would Professor Sands’ access to evidence and ICC deliberations create an asymmetrical access to information within the ICSID tribunal and in respect of other arbitrators?[13]
III. Holding
The Unchallenged Arbitrators accepted the Claimant’s Proposal to disqualify Professor Sands. They held that actual dependence or actual bias did not need to be proved. Under Articles 57 and 14(1) of the ICSID Convention, proof of actual dependence or bias is not required. Actual dependence or bias did not need to be proved; an appearance of dependence or bias was sufficient, provided that the lack of the required qualities was “manifest”, meaning “evident” or “obvious”. It must be objectively evaluated by a reasonable third party. A challenging party’s concerns are not enough on their own; they must be supported by objective evidence.[14]
An arbitrator serving in parallel proceedings does not by itself establish prejudgment or unconscious bias. It was held that arbitrators may still hear separate cases involving similar facts, legal questions, witnesses or measures without necessarily losing their independence or impartiality.[15]
Here, the decision rested on the combined effect of several circumstances: Professor Sands would hear many of the same witnesses, review related documents concerning the same asset, and take part in confidential ICC deliberations before the evidence was considered in the ICSID arbitration. In those circumstances, a reasonable third party would perceive an obvious risk that impressions formed in the ICC arbitration could influence Professor Sands’s assessment of the ICSID case.[16]
The Unchallenged Arbitrators concluded that Professor Sands’ continued participation would create an imbalance within the ICSID tribunal. They disqualified him and reserved the question of the costs arising from the Disqualification Proposal for a later stage.[17]
IV. Reasoning
The Unchallenged Arbitrators first set out the standard ICSID test: independence and impartiality are to be assessed objectively, from the perspective of a reasonable third party, and the lack of the required qualities must be “evident or obvious”. Impartiality concerns the “absence of bias” towards a party, while independence concerns the “absence of external control” or influence.[18]
The arbitrators initially rejected the proposition that overlap alone justified disqualification. Similar facts, recurring legal issues or overlapping witnesses are common. Moreover, Professor Sands’ experience and reputation supported the view that he could separate the cases since Professor Sands had extensive experience. The Claimant had submitted no evidence suggesting that Professor Sands had failed to decide previous proceedings independently and impartially.[19]
The Unchallenged Arbitrators did not question Professor Sands’ ability to assess the facts, testimony, and legal issues fairly in both proceedings. Rather, their concern was that his prior exposure to the evidence in the ICC Arbitration could unconsciously affect his assessment of the ICSID case.[20] They considered that his early exposure to contested evidence presented by the same counsel and involving many of the same factual and expert witnesses could shape his subsequent perception of that evidence and those witnesses, even without any conscious attempt to transfer information from one proceeding to the other.[21]
That concern was particularly acute with respect to the overlapping witnesses. Because those witnesses were expected to testify first in the ICC Arbitration, Professor Sands would already be familiar with their evidence by the time they appeared in the ICSID Arbitration. He would have observed their presentation, heard their examination and cross-examination, and assessed their credibility in another adjudicative context. The other members of the ICSID tribunal, by contrast, would encounter their testimony for the first time.[22]
The Unchallenged Arbitrators emphasised that the concern went beyond access to the same documentary record. Direct and cross-examination, and the context in which evidence is presented, could affect both its interpretation and the assessment of credibility. Placing the ICC record before the ICSID tribunal would therefore not give the other arbitrators the same impressions that Professor Sands had formed while hearing the evidence in the ICC Arbitration.[23]
Another concern was that Professor Sands would be exposed to his ICC co-arbitrators’ views of the evidence. He would hear their private assessments and impressions during the ICC tribunal’s deliberations, giving him access to perspectives that the Unchallenged Arbitrators could neither examine nor evaluate. As those deliberations would not form part of the ICC evidentiary record, the concern could not be resolved by placing that record before the ICSID tribunal.[24]
The fact that Buried Hill was represented by the same counsel in both proceedings did not solve the problem. The concern was not whether the parties’ legal teams had access to the same information, but whether all three members of the ICSID tribunal did. Each arbitrator needed to decide the case on broadly the same evidence and impressions.[25]
Finally, the Unchallenged Arbitrators acknowledged that the need to avoid asymmetry within the tribunal took precedence over preserving Turkmenistan’s autonomy to select its arbitrators. Indeed, although Turkmenistan’s freedom to appoint its preferred arbitrator was an important consideration, party autonomy could not override the need for all members of the tribunal to decide the case on broadly the same information.[26]
V. Conclusion
The Decision does not establish a general prohibition against arbitrators serving in parallel or related proceedings. The Unchallenged Arbitrators expressly accepted that factual or legal similarities, repeated witnesses and even overlapping parties may be compatible with an arbitrator’s continued service. In this case, the Decision was fact-specific.[27]
The Decision shows that conflict concerns may still arise even when the claims in the two proceedings are legally distinct, particularly where they rely on much of the same evidence. The same witnesses and documents, the order in which testimony is heard, the common underlying asset and an arbitrator’s access to confidential deliberations may together create a risk of unconscious influence and leave the tribunal members with different information.[28]
Conflict analysis should not stop at comparing party names, causes of action or governing instruments. It should also examine the expected witnesses, documents, hearing chronology, confidentiality obligations and likely flow of information between proceedings.[29]
Most importantly, the Decision treats equality within the tribunal as a substantive component of arbitral fairness. Even where there is no finding of actual bias, and even where the challenged arbitrator is as experienced as Professor Sands, the integrity of the process may require disqualification when one tribunal member is likely to possess materially different, untestable impressions arising from another proceeding.[30]
[1] Buried Hill Serdar Limited v. Turkmenistan, ICSID Case No. ARB/25/40, Decision on the Claimant’s Proposal to Disqualify Prof. Philippe Sands, 11 February 2026, ¶¶ 1-2, 17, 79-83, 114.
[2] Id. ¶¶ 91-100, 101-114.
[3] Id. ¶¶ 23-24.
[4] Id. ¶¶ 18, 25, 42.
[5] Id. ¶¶ 19, 39, 52, 61.
[6] Id. ¶¶ 27, 105-106.
[7] Id. ¶¶ 19, 25-28.
[8] Id. ¶¶ 7, 18, 37, 100, 104.
[9] Id. ¶¶ 35, 41-45, 48-51.
[10] Id. ¶¶ 52, 61, 63, 66-68.
[11] Id. ¶¶ 70, 72-75.
[12] Id. ¶¶ 90-100.
[13] Id. ¶¶ 101-113.
[14] Id. ¶¶ 80-81, 84-89, 114(a).
[15] Id. ¶¶ 92, 94-97.
[16] Id. ¶¶ 100, 102, 104-110.
[17] Id. ¶¶ 111-114.
[18] Id. ¶¶ 84-89.
[19] Id. ¶¶ 92, 94-97.
[20] Id. ¶¶ 99-100.
[21] Id. ¶¶ 100, 104-106, 109.
[22] Id. ¶¶ 104-105, 109.
[23] Id. ¶¶ 102, 107, 109.
[24] Id. ¶¶ 102, 107, 110.
[25] Id. ¶¶ 101-103, 108.
[26] Id. ¶¶ 101-102, 111-113.
[27] Id. ¶¶ 92, 94-100.
[28] Id. ¶¶ 100, 102, 104-110, 113.
[29] Id. ¶¶ 94-97, 102, 104-110.
[30] Id. ¶¶ 98-103, 109-113, 114(a).
