used2bedomestic

I have been trying to locate info about certain fuel companies. I tried searching on the internet to find out who makes Costco brand gasoline and have had no luck.
Does anybody know where I might find info about who makes what fuel? If not, maybe a link or webpage?
I am working on a research project and could use some help.
BTW, I live in California. I know that makes a little bit of difference due to the way fuel is refined in California.
Thanks.