I have a 2015 Acura ILX 2.0 and it says in owners manual 91 Octane Minimum .. Mid grade is 89 and Sunoco has 91 and 93... Sunoco is the only place that has 91 and what crazy is the 91 octane costs more then the 93 ULTRA.,,, Anyways... Most places have 86 regular and 89 Mid-grade and 93 Premium. I tried 86 Octane when I first bought the car and it ran fine but I have been told that it will cost me in the log run... So I have been using 93 Octane... However the HONDA CIVIC is basically the same as the ILX.. I'm pretty sure its the same spark plugs and coils if you look up the same year and engine.. I have not done that yet but Im going to . However the ACURA Says on the gas tank door PREMIUM FUEL ONLY... Not Recommended.... Says ONLY... Can anyone explain why??? Thanks P.S Also I was told not to use Regular / 86 and then put Octane booster.... That would be bad to do with each fill up.