Premium diesel in my area is 47 cetane regular is 40. Premium should have additives, but i'm reluctant to pay the higher price.64oz of Stanadyne treats 250 gallons or 8oz treats 30 gallons.They claim up to 5 point cetane gain but how much. So what I do is put 4oz of Stanadyne per tank. I mainly use it because it cleans and lubricates and it does cut down on smoke. To fill up with premium and use stanadyne seems like overkill because Stanadyne upgrades and stabilizers fuel so no need to buy premium.