Nice car! I hope you got dynamic cruise control that keeps a set distance from cars in front of you. AND lane keeping assist that works when the cruise is on. I loved that feature on interstate highways, it will turn for you!

Now, for your 2007 S80. The Volvo manual says this about fuel:

"Octane rating
Volvo engines are designed to achieve rated horsepower, torque, and fuel economy performance using premium 91 octane fuel.

Volvo recommends premium for best performance, but using 87 octane or above will not affect engine reliability.

In demanding driving conditions, such as operating the vehicle in hot weather, towing a trailer, or driving for extended periods at higher altitudes than normal, it may be advisable to switch to higher octane fuel (91 or higher) or to change gasoline brands to fully utilize your engine's capacity, and for the smoothest possible operation."

So, unless you are racing, use regular.
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Keeping it running is better than buying new