I just found this little bit of information on a pretty cool site
http://www.nissaninfiniticlub....shtml
Industry uses different methods in differnt parts of the world to determine Octane readings.
In the US we use an average of RON ( research ocatne number) and MON (motor octane number).This results on somwhat lower numbers listed for US octane ratings.In Australia I presume the same system is used as in Europe where premium is also 98 octane ( or 99 sometime).
RON or MON or different ways of looking at octane ratings in diffrent driving conditions they ra enot just "one higher/lower" than the other and then to be averaged.
So the 98 octane listed in Europe/Australia does not mean what 98 would be here.It would be rated as less in the US calculation system.
-scott