"Top tier" is a voluntary industry labeling standard regarding fuel quality, especially additives. It was implemented by several major brands such as Shell at the request of BMW, Mercedes, Porsche and perhaps others to insure that their vehicles had available to them a high quality fuel. Anyone posting the top tier logo has to meet certain specs. Some of the major gas companies refused to do this but still provide high-quality fuel. Google it for more information. The point is that over time a higher-quality fuel is better for your vehicle than a lower-quality one, although you pay more. This has nothing to do with octane rating. I would spend my money there before worrying too much about octane rating, but if the prospect of a little power loss is troublesome to you or, for you, inconsistent with a quality vehicle, then buy the higher octane. I notice no difference on the road in MPG or performance during normal driving. In my race car, where performance really matters, I would never buy less than 110.
Last edited by dcharnet; 02-23-2013 at 12:25 PM.