Milage and performance with higher octane-2012 Volvo S60 T5

to gain any advantage from a higher octane gasoline would require a different program in your computer.

Actully, according to the 2012 Volvo S60 T5 Manual, "Volvo recommends using premium unleaded gas for best performance, but using 87 octane or above will not affect engine reliability. Volvo engine is designed to achieve rated horsepower, torque, and fuel economy performance using premium 91 octane fuel." Chapter 06, Refueling; p. 253

In my 2012 S60, the check engine light comes on when I use premium fuel.

That sounds like a possible issue with your evap system. Do you know what codes are being thrown by the cel?

George the S60 depending on which engine you have has 250 horsepower and 258 foot pounds of torque but as you go up in size in motor you go up in horsepower up till 316 and then 400 for the T 8 and depending on how much your car weighs etcetera etcetera I'm sure you can figure it out

And Eddie is your gas cap ventilated