The Ninth Circuit affirmed the district court’s judgment in favor of Exxon Mobil Corporation on AECOM Energy & Construction, Inc.’s appeal regarding three post-trial rulings. First, the court upheld the grant of judgment as a matter of law under Federal Rule of Civil Procedure 50(b) on AECOM’s claim for violations of the Montana Prompt Payment Act (PPA). Applying a de novo standard of review, the court held that no reasonable jury could find a PPA violation because the parties had contractually adopted alternative billing procedures in their Purchase Order that superseded the Act’s default monthly cycle. The evidence showed Exxon exercised its contractual right to set off damages against payments within the agreed thirty-day period for four invoices, and AECOM failed to establish submission dates for the remaining two invoices; consequently, there was no evidence of a delay exceeding thirty days required to trigger PPA penalties. Second, the court affirmed the district court’s interpretation of the jury verdict form, rejecting AECOM’s argument that it was entitled to additional sums based on the now-invalidated PPA claim. Third, the court affirmed the denial of prejudgment interest, applying Montana state law which requires that a monetary obligation be capable of being made certain and vest on a particular day. The court determined that due to the complex nature of the dispute involving competing expert valuations and significant factual disputes regarding damages, the amount of recovery was not ascertainable until the jury returned its verdict, rendering prejudgment interest inappropriate. As a result, the district court’s judgment stands, and all pending motions are denied as moot.