I always wondered that too. I think the only difference is that some gas companies have there own additive in the fuel, (i.e. Chevron has Techron, 76 has pro-power, etc) So i think gas is gas since it has to meet a state to state requirement but then some fuel companies go an extra more by adding fuel enhances for better gas mile or cleaner burning fuel. You have to ask your self, why you the second gas station sale the same gas for so much less? BTW I pump 16 gal in my C43 @ $2.29 ~$36.00 every 3 days.