[MikeLee2484]

im going to say only use the grade of gas that is recommended. dont use a lower or higher grade than what it says. the reason for this is that cars are designed to run with a certain grade of gas. if you use lower grade, you wont get the performance you should get, and if you use a higher grade nothing will happen except money leaving your wallet when it doesnt have to. like i said, cars are designed to run on a certain grade, and so you wont get the performance or gas mileage you would like out of your car when you use a lower grade. and, like what was said before, if you use a much lower grade gas, there is a chance that you can cause some damage. so just use the 91, youll be happier in the end. and besides, what advantage does audi get if you have to put 91 in your tank? they arent getting more money because of it, there is no conspiracy with the oil/gas companies. and for the oil, there should be a guide in the manual of the car that tells you what oil to use in what weather conditions, just follow that.