I was at a Clark station last night that had 5 grades of gasoline.
87 89 90 91 91
I can't figure out why there were two 91 grades, both the same price. The pump seemed to indicate there was 10% ethanol in all five, but not what the difference in 91'* was.

YOu got me on this one. The Clarks that I have seen had 93 for thr high. All of the pumps had two 91'*? THat is strange.

My only guess was this particular station used to have 93, but decided not to carry it anymore, but still use the tanks for 91. If it were me, I'd put 87 or 89 in them, because they are more popular fuels.

Wow! That brings back memories of the 60'* and 70'* when Sunoco produced 7 grades of leaded gasolines starting with Sunoco 190 with around 89 octane to the fabled Sunoco 260 that produced over 98 octane(I think they skipped Sunoco 250). Back then Sunoco 190 could not run effectively even in a VW Beetle(REAL Poor Mans Gas). The only cars that could use the power of Sunoco 260 were the big block Corvettes, Chrysler Hemi'*, GTO'*, et al.