Why courts now expect quantum experts to show their working: Santos v Fluor
The Queensland Supreme Court’s decision in Santos Ltd v Fluor Australia Pty Ltd is a timely reminder that expert evidence on quantum must do more than state conclusions. It must explain, transparently and logically, how those conclusions are reached.
The case involved large and complex construction claims. The scale of the dispute, however, did not relax the evidentiary standard. If anything, the Court made clear that complexity increases the need for clarity.
The consistent theme running through the judgment is simple. A court cannot act on an opinion unless it can see the reasoning that supports it.
Courts must be able to see and test the reasoning
At the centre of the Court’s analysis is the requirement that an expert expose the foundations of their opinion. Adopting orthodox evidentiary principles, the Court stated:
“The facts upon which an expert’s opinion is based must be available for scrutiny by the tribunal. A court can hardly be expected to act upon an opinion the basis for which is not explained by the witness expressing it.” ([259])
Santos Ltd v Fluor Australia Pt…
That statement goes to the heart of modern quantum evidence. It is not enough to say that costs were incurred or inefficiency occurred. The court must be shown the factual building blocks and how those blocks lead to the final figure.
Assumptions must be identified and supported by evidence
The Court also reaffirmed the basis rule. An expert opinion has no value unless the assumptions on which it rests are capable of being proved. As the Court explained:
“An expert opinion is not admissible unless evidence has been, or will be, admitted… capable of supporting findings of primary fact which are sufficiently like the factual assumptions on which the opinion is based to render the opinion of value.” ([258])
Santos Ltd v Fluor Australia Pt…
For quantum experts, this is a direct warning against global claims, rolled up allowances and unexplained percentages. If the factual assumptions are not identified and proven, the opinion is exposed to attack at a fundamental level.
Methodology matters more than labels
A striking feature of the judgment is the Court’s focus on methodology. The Court accepted quantum evidence where the reasoning process was laid bare. That included identifying relevant cost categories, validating records against contemporaneous project material, and applying stated principles consistently.
The Court emphasised that key conclusions were reached by calculation, not assertion. Opinions were supported by arithmetic and analysis that could be followed and tested, rather than by experience alone ([268]–[271])
This reflects a broader judicial trend. Courts are less interested in the label attached to a methodology and more interested in whether the reasoning is coherent, evidence based and logically connected to the outcome.
Disagreement with reasoning is different from lack of foundation
The judgment also draws an important distinction between two very different types of criticism. The Court noted that where an expert’s assumptions are proven and the methodology is explained, disputes about the reasoning process are matters of weight, not admissibility:
“The real criticisms… are attacks on his reasoning process. They have nothing to do with the basis rule.” ([272])
That distinction matters. Unsupported assumptions undermine an opinion at law. Reasoned analysis gives the court something it can engage with, even if it is ultimately not accepted.
What this means for quantum experts
The message from Santos v Fluor is clear and practical.
Courts expect quantity surveyors to identify their assumptions, prove those assumptions with evidence, and explain step by step how costs are derived. Volume of material does not compensate for a lack of reasoning. Experience does not replace analysis. Conclusions without working are unlikely to survive scrutiny.
Quantum evidence succeeds when the court can see how the figure was built. It fails when the answer is presented without the working.
That is no longer a matter of style or preference. It is now a matter of evidentiary discipline.
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