After working in an Australian fuel terminal for just over four years now as an operater and seeing the changes in fuel colours, densities and performances I've found out a lot about the pros and cons but my own opinion (take it as you will) is far from what I first expected!! First off desiel is the most refined and pure fuels you can buy ( apart from aviation fuels of course) and a lot of work goes in to its combustiblity which I didn't realise and then there's ulp 91 which would have to be the lowest .. O there is one lower which is sugarcane based ethanol which is good in theory but attracts water like crazy which is not ideal special in servo tanks, then you got your 95's and last of all there's 98 ( call it what you will) but after seeing the corrosive sticker on additive which is added straight to your 98 I started to under stand why they do it , it is a cleaning agent just like what you would add to you normal fuel but after seeing what this additive does to valve gland packing, sensors and normal pipe work around the terminal after no product flow for awhile i was a bit unsure about the life span of cars using this 98 overall it does clean your fuel tank, fuel lines and engine really we'll but it's only early days and to see what it does to cars in the long run is any ones guess, so unless your vehicle recommends 98 octane for performances I would only use it maybe once a Month for and clean out 91 is still great to use as well as 95 but at the end of the day it all depends on the servo station,( never fuel up at the servo when there's a fuel tanker unloading for at least a day because they normally stir up the bottom of the tanks leaving suspended water and crap from the bottom of the tank and put in you tank which is not good, I hope that helps and if you have any questions please ask Cheers