Do I need to put higher octane fuel in my Volvo 2.5T?

Volvo suggests putting 91 octane in. Your knock sensor will detune the engine if you only use 87 octane. This will give you fewer horsepower and lower torque than the engine is capable of. Naturally, knock sensors sometime fail and that would result in a wrecked engine if you were just using 87 octane. Everytime you get to a half empty gas tank, you COULD alternate fill ups between 93 and 87 in the eastern US, resulting in a blended 90 octane. The difference between 93 and 87 octanes may be $.24/gallon. If you drive 10,000 miles/yr and got 22 mpg overall, that's 454 gallons/yr. If half those gallons cost an extra $.24/gallon to get 93 octane, than you'd pay an extra $55/year - about $1 per week. That's no big deal!