Gone are the days when district courts in the Seventh Circuit can grant class certification without resolving conflicting expert evidence. On Aug. 5, 2025, the U.S. Court of Appeals for the Seventh Circuit, in Arandell Corporation v. Xcel Energy Inc., held that district court judges cannot avoid rigorous expert analysis at class certification by deferring those questions to the merits phase of the case. Instead, judges must resolve key expert disputes at class certification. For companies facing class actions, this means a greater opportunity to challenge class certification by exposing weaknesses in the plaintiffs’ expert evidence.
What Happened in Arandell?
The plaintiffs in Arandell, a putative class of industrial and commercial purchasers of natural gas in Wisconsin, alleged that natural gas companies engaged in a conspiracy to manipulate prices nationwide from 2000 to 2002. The plaintiffs claimed that they paid inflated prices because of the defendants’ tactics, such as wash trading, churning and false reporting.
The Seventh Circuit vacated the previous class certification order and remanded the case to the district court for further proceedings. The Seventh Circuit found that the district court did not sufficiently engage with the conflicting expert testimony and economic models presented by both sides. The district court decided that both parties’ expert opinions were admissible but did not go far enough in critically evaluating the substance and reliability of those opinions, particularly as they related to the existence of a national market and the alleged common impact of the price-fixing conspiracy.
The Seventh Circuit identified as a shortcoming the district court’s failure to resolve material disputes between the plaintiffs’ and defendants’ experts. The Seventh Circuit emphasized that, at the class certification stage, it was not enough to acknowledge that both sides presented credible experts. The district court must rigorously analyze the competing economic models and make factual findings about whether the plaintiffs’ evidence is sufficient to show that common issues predominate over individual ones.
The Seventh Circuit also clarified that the district court cannot defer these determinations to the merits phase, even if the issues overlap with the ultimate questions to be decided at trial. The requirements of class certification under Federal Rule of Civil Procedure 23 demand a thorough and searching review of the expert evidence at this preliminary stage.
In its instructions on remand, the Seventh Circuit directed the district court to conduct a more detailed and rigorous evaluation of the economic models and expert opinions. The district court must resolve substantive disputes between the experts, make clear findings on whether the plaintiffs’ models can show classwide impact through common proof and address the complexities of the natural gas market as reflected in the voluminous expert reports. The Seventh Circuit suggested that counsel help the district court by organizing expert evidence in a clear and accessible manner, such as with flowcharts or guided presentations.
Implications for Practitioners
Below are a few practical takeaways from the decision that practitioners should consider when reviewing their class certification strategies:
- Structured and Detailed Presentation of Expert Analyses: Both sides should organize their expert evidence in a manner that is accessible to district court judges, who will have varying degrees of antitrust experience. Considering the Seventh Circuit’s suggested use of flowcharts or guided presentations, the parties should provide summaries, visual aids and clear roadmaps that highlight the main points of agreement and disagreement between the parties’ experts. The parties’ presentations must be clear and directly address the court’s concerns.
- Direct Engagement With Opposing Expert Critiques: The Seventh Circuit criticized the district court for not resolving material disputes between the parties’ experts. As a result, each side should ensure that they directly address the criticisms raised by the opposing experts. This could involve point-by-point responses, side-by-side comparisons of methodologies, and explanations of why certain critiques are unfounded or irrelevant. The goal is to help the court make factual findings about the reliability and sufficiency of each side’s economic models.
- Clear Distinction Between Admissibility and Adequacy: The Seventh Circuit emphasized that the district court must go beyond finding expert opinions admissible under the rules of evidence. The parties must present their expert evidence in a way that meets the threshold for admissibility and persuasively addresses whether the evidence is adequate to satisfy the requirements of Rule 23 for class certification. This may involve more detailed explanations of the underlying data, assumptions and limitations of each model.
- Anticipation of Evidentiary Hearings or Live Testimony: Given the Seventh Circuit’s directive for a more rigorous analysis, the district court may require live testimony from the experts or evidentiary hearings to resolve key disputes at the class certification stage. The parties should prepare their experts to testify in court, sit for direct and cross-examination, clarify their positions in real time and respond to questions from the judge. Experts must communicate complex economic concepts clearly and persuasively.
- Coordination With Co-Defendants and Joint Defense Groups: In cases with multiple defendants, it is important to coordinate expert strategies early. Consider whether to hire joint or separate experts and be ready to address inconsistent positions.
The Arandell decision makes clear that district courts in the Seventh Circuit must now resolve expert disputes head-on at the class certification stage, not defer them. For companies facing class actions, this means a more rigorous, evidence-driven process and a greater opportunity to challenge class certification by exposing weaknesses in the plaintiffs’ expert evidence. Early, thorough engagement with expert issues is more important than ever.
