CNOOC PETROLEUM NORTH AMERICA ULC v ITP SA, 2026 ABKB 582

This decision arose from competing Applications concerning expert reports in complex, multi-party pipeline litigation approaching Trial. After primary expert reports were exchanged, the parties served a number of rebuttal reports. Each side alleged that certain reports, characterized as rebuttal reports, were, in substance, primary reports that should have been served earlier under the Complex Case Litigation Plan (the “CCLP”). The parties also disputed whether one rebuttal report improperly duplicated other expert evidence and what surrebuttal reports could address.

Associate Chief Justice Nixon considered the sequencing of expert reports pursuant to Rule 5.35. Nixon A.C.J. confirmed that Rule 5.35 establishes a sequential process for the exchange of expert reports. The party bearing the primary onus of proof serves its initial expert report first. The other party or parties may then serve their rebuttal reports, which could include issues not raised in the initial report. Finally, the party that served the initial report may serve a surrebuttal report responding only to new issues raised in rebuttal.

The process promotes meaningful pre-trial disclosure and focuses the issues for trial. While a rebuttal report could raise new issues, it cannot be used to split a party’s case or merely confirm or reinforce evidence that should have been included in its primary report. The Court emphasized that Rule 5.35 was to be applied as a fair and workable process for disclosure rather than through an overly rigid or expansive interpretation.

In considering the “primary onus of proof” under Rule 5.35, Nixon A.C.J. held that the inquiry depended on the circumstances of the particular case and the specific issue on which the expert evidence was tendered. The Court rejected a rigid interpretation of the Rule and held that, although a defendant might bear the burden of proving a defence such as contributory negligence, that did not necessarily require an expert report concerning that defence to be served as a primary report. Applying this approach, the Court held that the challenged reports had properly been served as rebuttal reports. Nixon A.C.J. further held that, even if the reports had ventured into matters that should have been addressed in primary reports, striking them would have been an inappropriate remedy where any resulting prejudice could be addressed at Trial or through costs.

Nixon A.C.J. also held that Rule 8.16 did not prohibit all overlap among a party’s experts. The Rule was intended to prevent the abuse, expense, and delay associated with unnecessary duplication of expert evidence, but a broader issue could encompass multiple distinct subjects requiring different expertise. In complex litigation, some overlap was unavoidable where experts addressed common subject matter from the perspective of their distinct training, experience, and expertise. The Court declined to strike the challenged rebuttal report because the expert’s expertise was sufficiently distinct from that of the party’s other experts and the evidence was not improperly duplicative.

With respect to surrebuttal reports under Rule 5.35(2)(c), Nixon A.C.J. held that whether a matter constituted a “new issue” depended on the circumstances of each case and declined to establish an exhaustive definition or framework. A surrebuttal report could respond to an alternative theory or new dimension raised in rebuttal and could contain expanded discussion where reasonably necessary to address matters of which the primary expert would not have been aware. However, a surrebuttal report could not merely reiterate, expand, or emphasize the primary report, make new allegations, or be used to split a party’s case. The focus remained on whether the surrebuttal was carefully confined to genuinely new matters arising from the rebuttal report.

Finally, Nixon A.C.J. recognized that the sequential process under Rule 5.35 was designed primarily for conventional two-party litigation and was more difficult to apply where multiple parties had divergent interests. Because Rule 5.35 permitted the ordinary sequence to be altered by agreement or Court Order, the Court amended the CCLP to extend the deadline and permit certain additional surrebuttal reports. However, the Court declined to permit a party to serve a surrebuttal report in the form of a rebuttal report that could raise new issues, holding that the parties should instead focus on narrowing the issues as Trial approached.