By and large, they're pretty much the same. However:
- Detergent mix might be different
- the quality control of your super market might not equal the brand name pump (ie test the tanks for water, dirt, contaminants, etc).
However, I'd be more concerned routinely getting Ex gas from the same middle-of-nowhere gas station that gets little traffic than suburban supermarket gas. Once in a while while you have 1000 mi to go on a trip, that gas wont affect anything. But, sitting in your half filled tank everyday that ethanol will suck up moisture and even polymerize into gunk.
- Detergent mix might be different
- the quality control of your super market might not equal the brand name pump (ie test the tanks for water, dirt, contaminants, etc).
However, I'd be more concerned routinely getting Ex gas from the same middle-of-nowhere gas station that gets little traffic than suburban supermarket gas. Once in a while while you have 1000 mi to go on a trip, that gas wont affect anything. But, sitting in your half filled tank everyday that ethanol will suck up moisture and even polymerize into gunk.