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The Real Brands Behind Costco's Kirkland Products

6. Kirkland Signature Motor Oil: Warren Motor Oil
It's not a mystery who manufactures Kirkland's Signature motor oil. It's right there on the bottle: Warren Oil Company. Since you know it's quality motor oil, you can rest easy that you're making an informed purchase while still cutting costs. A two-pack of 5-quart Kirkland bottles costs $29.99 at CostCo, while a 1-quart MAG 1 bottle (another brand that Warren manufactures under) costs $40. 

Kirkland Signature 5W-30 Full Synthetic Motor Oil 5-quart, 2-pack, $29.99, Costco