Have you ever forgotten what side your gas cap is on your car? I used to mix up mine and my wife's car a lot since they have it on different sides. This may be common knowledge but I had never heard about this and lots of people I talk to also havent. When you look at your gas gauge and there is the little pump symbol. Somewhere around there there should be a little triangle that either points to the left or right. This denotes which side your gas cap is on. Because knowledge is power!