I'm surprised I don't find mobil on this list of top tier retailers.
QuikTrip
Chevron
Conoco
Phillips
76
Shell
Entec Stations
MFA Oil Company
Kwik Trip/Kwik Star
The Somerset Refinery, Inc.
Chevron-Canada
Aloha Petroleum
Tri-Par Oil Company
Shell-Canada
Texaco
Petro-Canada
Sunoco-Canada
I highly doubt that is your problem though. If that was the case I don't think any of them would be driving around here withoout the engine light on. I don't know of any top tier stations in my area.
