I think Kia tuned the engine to run on regular due to the highrer cost of premium fuel. This cars price is still a level where it is within reach of allot of peoples budget. That being said, this same group of people (me included) do not want to pay the additional $0.60 - 0.70 per gallion for premium. If I could afford a Porsche 911, or something similar I would not care about the extra cost. I was actually looking at a Stinger GT with the 255 HP 4 banger about a year ago, it does require the premium fuel. Just my 2 cents.Kia recommends regular unleaded for the 2.5T wich I find bizarre. I for one will be using shell 91.Any GT owners use regular? I'm assuming the hp gets bumped up closer to 300 with premium fuel.