This is interesting... though dated...
http://www.ftc.gov/opa/predawn/F93/sunoco.htm

Sun Company, Inc., and its subsidiary, Sun Refining and
Marketing Company, both of Philadelphia, have agreed to settle
Federal Trade Commission charges that they claimed Sunoco high-
octane Ultra 93.5 and Ultra 94 gasolines are superior to other
gasolines in providing engine power and acceleration, but did not
have a reasonable basis to back up these representations. The
proposed settlement agreement would prohibit any future unsub-
stantiated engine-performance claims for Sunoco gasolines.
According to the FTC's complaint, issued simultaneously with
the proposed consent agreement to settle the charges, advertise-
ments for Ultra 93.5 and 94 gasolines made the following state-
ments:
-- No other gasoline can give your car better acceleration.
Because no other gasoline has 94 octane; and
-- Because no other gasoline has 94 octane - the highest
octane under the sun....Don't waste your time going anywhere
else. Come to Sunoco and fill up with Ultra 94 - for
maximum power and performance.
Anyway, I'd believe Ultra 94 contains MBTE and oxygenated fuel. Wonder if that still holds true. Maybe I'll just run 91 at Petro and mix in some Toluene instead