Hello! I’m going to look at a 2006 S40 2.4i and was wondering if premium fuel is needed for this glorious vehicle. Thanks!!

 

I absolutely would use it. 10.3:1 compression

 

best reference is to use the owner's manual or the RON rating inside the filler door. Manufacturers are pretty specific by either stating the octane as "Recommended" or "Required" etc. Here's what the 2006 S40 owners manual says:

Octane rating
Volvo engines are designed for optimum performance on unleaded premium gasoline with an AKI octane rating 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).

US gas pumps display the RON+MON/2 number so there you go. Anything showing 91 or more at the pump is what you'd want.