Think octane ratings are different in the US. There is a thread on this going back a year or so.
Their 93 is our 97 or something like that..
We can only get 95 or 98 octane here in UK (as far as I am aware). I tend to mix them up a bit. I have a feeling that I get better mpg on the higher octane, premium, fuel (achieved 39.5mpg on a long run recently), but I haven't tested it properly. As you say, fuel costs just keep going up (there only seems to be one direction of travel, no matter what the crude price!).
regards
Peter