12. E&J Gallo wines

E. & J. Gallo Winery is a well-known American winery and wine distributor, and it ranks among the largest and most prominent wine producers in the world.

There is speculation that this brand may be the source of Costco’s wines, although this has not been officially confirmed yet. The speculation arises from an Alcohol and Tobacco Tax and Trade Bureau registry that links Kirkland Signature’s California wines to E&J Gallo Winery. 

However, this does not definitively prove whether E. & J. Gallo makes Kirkland’s wines or simply mediates wine purchases for Costco.