From the owner's manual:

Octane Rating



Volvo engines are designed for optimum performance on unleaded premium gasoline with an octane rating. AKI of 91, or above. AKI (ANTI KNOCK INDEX) is an average of the Research Octane Number, RON, and the Motor Octane Number, MON, (RON + MON/ 2).
The minimum octane requirement is AKI 87 (RON 91).



Gasoline containing alcohol and ethers



"Oxygenated fuels"
Some fuel suppliers sell gasoline containing "oxygenates" which are usually alcohols or ethers. In some areas, state or local laws require that the service pump be marked indicating use of alcohol or ethers. However, there are areas in which the pumps are unmarked. If you are not sure whether there is alcohol or ethers in the gasoline you buy, check with the service station operator.
To meet seasonal air quality restrictions, some states require the use of "oxygenated" fuel in certain areas.
Volvo allows the use of the following "oxygenated fuels; however, the octane ratings listed on this page must still be met.
Alcohol — Ethanol
Fuels containing up to 10% ethanol by volume may be used.
Ethanol may also be referred to as Ethyl alcohol, or "Gasohol".
Ethers — MTBE
Fuels containing up to 15% MTBE may be used.
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I am seeing many more engines with leaking head gaskets, in most cases it is heat related. These engines all have 150K+ miles on them and have used regular gasoline. Both turbo and NA. Unscientifically, I reasoned that the hotter fuel leaving the exhaust valve is creating excessive heat and causing the problem.
The NA engines have a compression ratio of around 10:1, which can easily cause detonation at lower rpms with low octane fuel.

Klaus
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