also,when a fuel delivery driver has too much of one type of gas it gets dumped into any tank that will hold it,cause they don't want to return with fuel in their truck due to the different blends and additives between gas stations,mid grade and high test or premium have additves such as dyes, detergents and stabilizer,according to Marathon I worked at.where all of regular unleaded is all the same,except clark who uses a red dye.