Federal Court Warns Against Experts who Criticise without Reporting their Alternative Findings

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Lawyers commonly ask experts to critique other experts’ reports, a move which recently received criticism in the Federal Court. We review Justice Yates’ comments on this approach in Sanda v PTTEP Australasia (Ashmore Cartier) Pty Ltd (No 7) [2021] FCA 237, and consider how lawyers and experts can avoid its pitfalls.

In March 2021, the Federal Court upheld a claim against PTT Exploration and Production Company Limited for its negligent management of the Montara Oil and Gas Field, which caused one of the worst oil spill disasters in Australian history and destroyed the seaweed crops of 15,000 farmers based around the Timor Sea. Several internationally renowned experts on oil spill chemistry, modelling, and environmental impact contributed expert testimony in the form of reports and cross-examination. Justice Yates’ comments on the approach of one of the PTTEP’s experts amounts to some important advice on expert reporting for experts and lawyers.


On 21 August 2009, a wellhead of the Montara Oil and Gas Field exploded and released oil and gas into the Timor Sea until 3 November 2009. The pouring of thousands of barrels of oil over the course of 70 days now counts as one of Australia’s worst oil disasters.

Earlier this year, the Federal Court upheld a claim brought by seaweed farmer Daniel Aristabulus Sanda on behalf of 15,000 seaweed farmers from the area around the Island of Rote, whose seaweed crops were destroyed by the failure of PTTEP (the responsible oil company) to safely operate the Montara wellheads. Justice Yates found that PTTEP owed a duty of care to the 15,000 farmers and that it had breached this duty when it performed the highly hazardous procedure of suspending the well and causing an explosion.

One of the key issues concerned the correct approximation for the volume of oil spilled as result of the exploded oil well. The applicants argued that the volume of oil released was in fact much greater than the amount claimed by the respondents (200 to 400 bbl/day). [254]

The Expert Evidence

Professor’s Werely’s evidence found that a more accurate approximation of the oil volume flow rate between 21 August 2009 and 31 October 2009 in fact amounted to 881 bbl/day. [173] His individual expert report cited the use of visual observations from photographs to calculate velocity of the oil and to assess the physical movement of the oil as it drifted downwards (due to gravity) and across the water (due to wind).

The Respondents engaged Dr Zaldivar to prepare a report which opposed Professor Werely’s findings. Dr Zaldivar, as per his instructions, critiqued Professor’s Werely’s evidence without offering an alternative methodology and calculations. He claimed that Professor Werely’s report was “completely unreliable and invalid” [263], based on four issues with the report, including: the failure to consider unknown variables in Mr Werely’s calculation of oil flow rate; a conversion rate error; and inaccurate assumptions about the exit angle of the oil from the well and the fraction of the well pipe that was filled. Dr Zaldivar also criticised Professor Werely’s reliance on low resolution photographs [269] and his failure to consider several other purportedly significant variables.

Professor Werely accepted the criticisms regarding the unit conversion and modelling of the rate and angle of ejection of oil. [277]-[279] However, the expert defended his use of photographs as a crucial part of his methodology which conformed with “commonly used methodologies in the open channel flow field (the study of flows in partially filled conduits, pipes and the like)”.[280] Professor Werely went on to provide an amended table of calculations. The new approximation for the total oil spill volume far exceeded his initial estimation: between 6,000 to 9,000 bbl/day.

As a part of the joint report with two other experts, Dr Zaldivar continued to criticise Professor Werely’s amended report but withheld offering alternative methodology and findings. [288]

Decision and “Sniper” Approach

The court concurred that the volume of the oil spill likely far exceeded the amount suggested by the Respondents.

In forming this conclusion, Justice Yates highlighted the relative strength of expert evidence which offers a substantive conclusion on the relevant issue of fact rather than merely offering a critique of the methods and conclusions of other reports. The court accepted Professor Werely’s revised calculations as a reliable approximation of the volume of the oil spill, with emphasis on the broad agreement of other experts that his  methods and conclusions were appropriate and correct.

The Court’s analysis of the relative merits of Dr Zaldibar and Professor Werely’s evidence included a significant warning about the cost of engaging an expert for the purpose of only providing a critique of other expert reports. The strategy amounts to what the courts have already identified as the “sniper” approach, in which an expert performs the work of “firing shots” at other experts’ evidence without providing his own substantive expert report and findings. [295]

Justice Yates warned that where an expert’s criticism does not fatally undermine opposing evidence in its first attempt, an expert’s whose only role in their evidence is to critique the reports of his peers is disadvantaged by the apparent lack of weight behind his own expert perspective on the matter. Without clearly outlined alternative methodology and findings, criticism of expert evidence usually fails to completely substantiate the impact of errors in the evidence and therefore fails to properly engage with the issues of fact. With respect to Dr Zaldibar’s evidence, Justice Yates commented:

[T]he main thrust of his criticisms was to raise the prospect of error, without demonstrating that there was error, or error that would lead to an appreciably different outcome in actual result. Thus, his contentions that Professor Wereley’s calculations were “unreliable” or “invalid” reside in, and do not transcend, the realm of argument and debate. [292]

The sniper approach is rendered especially ineffective where courts allow experts to simply integrate valid criticism by rectifying or amending reports, and where expert testimony purports only to provide an approximation in its findings or articulates its own limitations.  In those cases, as in Montara, criticism of amended evidence not only flies in the face of the Court’s objective of “just, quick, and cheap” solutions, but are prone to point redundantly to limitations of the expert evidence already apparent to the court.


  • Avoid the sniper approach when you can. Lawyers engaging expert witnesses for the purpose of critiquing of opposing expert evidence should also request an expert report which provides in detail the methodology, calculations, and findings of the expert witness. Experts should be prepared to provide a complete report of their reasoning and findings.
  • When contributing to a joint report and conclave, experts should be prepared not only to outline their differences of opinion, but also present a complete account of their own reasoning, methodology and different findings if there are any.


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