The Energy Information Administration (EIA) cannot definitively say where gasoline at a given station originated since EIA does not collect data on the source of the gasoline sold at retail outlets. The name on the service station sign does not tell the whole story. The fact that you purchase gasoline from a given company does not necessarily mean that the gasoline was actually produced by that particular company’s refineries.
Gasoline Brands Get Mixed During Shipment

While gasoline is sold at about 162,000 retail outlets across the Nation, about one-third of these stations are "unbranded" dealers that may sell gasoline of any brand. The remainder of the outlets are "branded" stations, but may not necessarily be selling gasoline produced at that company’s refineries. This mixing of brands occurs because gasoline from different refineries is often combined for shipment by pipeline, and companies owning service stations in the same area may be purchasing gasoline at the same bulk terminal.

The only difference between the gasoline at station X and the gasoline at station Y may be the small amount of additives that those companies add to the gasoline before it gets to the pump.
Crude Oil also Gets Mixed at the Refinery

Even if we knew which company’s refinery produced the gasoline, the source of the crude oil used at that refinery may vary on a day-to-day basis. Most refiners use a mix of crude oils from various domestic and foreign sources. The mix of crude oils can change based on the relative cost and availability of crude oil from different sources.