is the quality of gas as good as chevron? my car is a bmw

I would say it is as good, if not better than Chevron. From their website: "Kirkland Signature™ Gasoline contains five times the EPA detergent requirement in both regular unleaded and premium grades, and is formulated to clean your engine and help your vehicle run like new." https://www.costco.com/fuel-promise.html

Better than Chevron, I only get gas at Sam's Club or Costco

I think, better than Chevron.