It depends on your location. Could be a number of blenders. Warren Distribution, Amalie, Warren Oil, Omni. It is whoever won the contract.
Flip the bottle over and look for a bottle stamp or ask for a SDS. Private label oils are quality products that meet the same API/ISLAC specifications.
The API and PQIA test and certify that you are getting a quality product. They are generally cheaper because you are not paying for marketing and CEO's new summer villas.