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Is Costco Top Tier certified?

Yes both grades of gasoline sold at Costco meet and exceed Top Tier requirements. The owner’s manuals provided by the following manufacturers recommend using Top Tier gasoline to maintain optimal engine performance. and efficiency.

BMW, including Mini Cooper and Rolls Royce
General Motors, including Buick, Cadillac, Chevrolet and GMC
Honda, including Acura
Toyota, including Lexus and Scion
Volkswagen/Audi, including Porsche, Lamborghini and Bentley
Mercedes-Benz, including Smart

Where does Costco get its gasoline?

Costco buys fuel from major refineries and distributors in each area. All Kirkland Signature™ Gasoline is fully guaranteed, just like the merchandise inside the warehouse.

https://www.costco.ca/gasoline-q-and...rue&langId=-24