In Australia they used to call the petrol Optimax and they claimed it
had a higher energy density than normal petrol. Now it is called V
Power - same octane rating - 95. for a while they were also selling a
V plus which contained ethanol (totally without any utility for the
user but tied up to some grubby politics in Oz). We usually use
optimax/V-Power but I have never detected and difference (and one,
early on, I  filled the tank with normal unleaded by mistake  - again,
absolutely no difference - or none that I could detect - but I
understand that the anti-knock system may have been operating
unobtrusively and reducing power or economy - maybe)