I have an 97' E320(Straight 6 cyl) and a 99 ML320 (V6). The Owners manual indicates they both need 91 octane fuel. Locally we have 87, 89 & 93 Octane. I have been putting 93(we dont even have 91 here) in them and they both run fine. My question is, do I REALLY NEED to put in the 93, or does anyone think I can get away with putting in only the 89 or even the 87. Obvioulsy, if money was no object I would not even be posting this question, but if I REALLY dont need this extra octane and expense I would rather not use the higher octane. I have not tried using the lower octane yet, as I was going to see what others had experienced here before trying it. Could/would using the lower octane cause damage in anyway? I understand I may lose a bit of power, but probably not enough to notice and if there was pinging or obvious loss of power I would go back to the higher octane. We use the cars for mostly around-town driving. Thanks in advance for your help! Mark