However, there is no evidence that India's Judge Dalveer Bhandari, who was re-elected last week for another nine-year term, ever worked as an arbitrator, according to the report published by Canada-based International Institute for Sustainable Development (ISSD).
The Statute of the ICJ prohibits judges from engaging "in any other occupation of a professional nature."
This probably explains the reason for Justice Bhandari consistently receiving nearly two-thirds of the votes in the UN General Assembly, and Justice Greenwood lagging far behind.
"Justice Bhandari as a matter of conscious choice does not do any arbitration cases," informed sources told PTI as the ISSD report threw staggering details of moonlighting by current and past judges of The Hague-based world's top court.
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The study found that Greenwood worked as an arbitrator in at least nine investment arbitration cases during his tenure at the ICJ. He was paid more than USD 400,000 in fees in two of those nine cases.
A total of more than USD 1 million in fees was paid to ICJ judges in nine of the 90 such cases compiled by ISSD.
The full amount is unknown because arbitrator fees are typically not disclosed in investor-state dispute settlement (ISDS) cases in which sitting ICJ judges have workedor are currently workingas arbitrators.
The true number may be higher given that many ISDS cases are not public, the report said.
"We are not questioning the integrity of the judges who are being pulled into these other functions," said lead author Nathalie Bernasconi-Osterwalder, director of IISD's Economic Law and Policy Program.
"The ICJ is the world's most important and respected court charged with the sound administration of international justice. Its representatives need to be held to the highest standards of independence," Bernasconi-Osterwalder said.
Expressing disappointment over the ICJ judges working as arbitrator, Gus Van Harten, a professor at York Universitys Osgoode Hall Law School whose research focuses on international investment law, said the ICJ is the preeminent international court, whose judges must strive to protect the court from appearances of bias tied to investment treaties.
ICJ's 15 judges are elected by UN member states for nine-year terms.
According to the report, nearly half of the ICJ's current members have worked as arbitrators during their tenure. Three of those judges each worked as arbitrators in nine cases. Of those 27 cases, fees were disclosed in nine of the concluded cases and amounted to USD 1.1 million.
"To our knowledge, there has never been a formal challenge against an ICJ judge for taking on an arbitration case based on the prohibition to 'engage in any other occupation of a professional nature.' According to the Statute of the ICJ, it would fall on the court itself to settle 'any doubt on this point'," the report said.
It said that during his current tenure as ICJ judge, Judge Greenwood was arbitrator on five cases.
Notably, the ICJ pays each judge an annual salary of roughly USD 173,000 (as of 2016), plus a post-adjustment allowance for living and working in the Netherlands.
The president of the ICJ receives a special supplementary allowance of USD 15,000. All amounts are tax free.
After leaving the court, judges receive an annual pension equal to 50 per cent of the annual base salary.
In addition to the five-closed case, Judge Greenwood continues to be arbitrator on four current cases.
The report reveals that Britain's Judge Rosalyn Higgins, who was an ICJ judge from 1995 to 2009, was a presiding arbitrator in India vs Capital India Power Mauritius I and Energy Enterprise (Mauritius) in 2003.
Band Judge Sepulveda-Amor from Mexico (2006-2015) was arbitrator for Bycell (Maxim Naumchenko, Andrey Polouektov and Tenoch Holdings Ltd) vs India in 2013.