Who is the major gas supply for the gas station at Costco ?

Question

In California ?

Answer 1

Most gas distributors get their stock from the same place, so it doesn't matter who their supplier is. I get gas from Costco all the time and see two or three different names on the tankers I see there filling  up their underground tanks. They're all local distributors, so the suppliers at one Costco won't be the same for the suppliers at another Costco in another state.

Answer 2

The trucks are just the carriers, not the actual branded gas suppliers.