While Costco is the primary retailer of Kirkland Signature Synthetic Motor Oil, it is not its manufacturer. Like all Kirkland products, the motor oil is instead farmed out to a separate manufacturer before being put on store shelves. That distinction belongs to Warren Oil. While Warren carries a handful of its own retail brands such as Gold Brand and Lubriguard, it is most well known for providing a wide range of greases, lubricants, and chemicals to various retailers.
When looking at Kirkland Motor Oil, the brands it is most comparable to are Walmart’s Super Tech and Amazon Basics Synthetic Motor Oil, both of which are also manufactured by Warren Oil. These oils meet similar specifications and standards from across the industry while also performing well in a variety of tests. The trusted YouTube channel Project Firm pitted Kirkland against Super Tech in a series of extensive and rigorous tests for evaporation loss speed, cold temperature flow, film strength, and more. In the end, both came extremely close in every category. This shouldn’t come as a surprise, as both brands come from the same manufacturer and are likely made from similar components.
