Ok, if they advise it then that makes a change, however i would be more interested in whether the increases do warrant the increase in price, i completely agree MonkeyHanger, if the fuel gives you a greater %increase in your desired trait, be it power or more fuel economy do it. But i seem to remember watch a video where the increases were small, and with one companies fuel, none. Im not saying i wouldn't adhere to the advise and put a higher octane in every so often, my dad does one tank premium for every 3 normal, i think id follow that sort of approach maybe. It pyschologically stings more when you break the £100 on a tank (80 litres in the cls63 and was 100 in the aston) it brings a tear to your eye. but with fuel cheaper at the moment this isn't such a problem