Subtract gasoline sales from Costco's same-store sales numbers, and the SSS number was 0.5% lower for the month of November, and 0.1% lower for all of Q1 -- but the same for the last 12 weeks. So basically, Costco got a bit of a boost from gas sales in November, but overall it was a wash.
https://www.fool.com/investing/2025/12/04/why-costco-stock-dropped-today/