Toxic-tort causation: Fifth Circuit affirms exclusion of experts

On October 27, 2026, a divided Fifth Circuit affirmed summary judgment for BP in DuFour v. BP Exploration & Production, Inc., a case brought by a Deepwater Horizon cleanup worker who alleged that exposure to crude oil and chemical dispersants chronically worsened his preexisting asthma. The court concluded that DuFour’s alleged injury fell within the category of non-readily observable injuries, or injuries with multiple possible causes, for which admissible expert testimony was necessary to survive summary judgment on legal causation. It held that the district court did not abuse its discretion in excluding the opinions of DuFour’s two causation experts and that, without admissible expert evidence, summary judgment for BP was proper. Judge Andrew Oldham dissented, questioning the applicable substantive law and the exclusion of the expert testimony.