ok its what gets the best mileage with way to find this out is by testing a few brands and types way to do this is by filling up at place you alway stop buy best they have set mileage or writ eit down drive til one need to fil agian buy next type write mileage down one gets you the most miles the one to use at that place then stop at place you sometimes stop do the same not al gas is the same and not all cars are drove the same so its up to driver to know which one gets the best fuel from and only way is to test a few types its like my nissan gets great mileage with shell high octane but gets the same with mobil regular mostly high the octane better the car runs better the mileage but knowing which fuel is best you have to test a few out better to get it where you always stop so one doesnt have to go out of way start with th ehighest ocatne at any places you go to will get you the best you can get then lower octane type wil show up if it dont get better mileage with it you wil see by the miles you drive with one