A lot of people only have 89 and 91 octane available. I think they use the 91 octane. I have 93 octane available in my local so that's what I use. It has much more ingredients to fight sludge, carbon buildup, engine knock, and so on, so for as little as I drive my XF, I prefer to use the 93. Shell V-POWER. I also only buy my gas at a Shell station. Some other brands may be just as good but, again, my preference is for Shell 93 octane. The car runs beautifully, has not met a hill that it can't level, and the exhaust pipes are very clean. I also use one of Needswings oil catch cans. Everybody should have those on their engine. Car runs much better.

Just my humble opinion.

Jim