Gasoline expansion has been in the news recently. I don't know exactly how much of an effect it has, but I think it's certainly worth considering.

Basically, people are realizing that 'stuff expands when heated' applies to gasoline. During warm weather, a gallon of gas is less has than during cool weather, and vice versa. To avoid losses due to shrinkage in cold weather, the oil industry has added meters on their pumps to adjust for the cool temperature. Yet they oppose doing the same in the US to adjust for the hot weather, as warm weather costs customers money to the benefit of the seller.

So what should we do? Only buy gas in the Winter? Obviously, this isn't an option for most people. But I will be trying to make my purchases on cooler days, and early in the morning or at night. Avoid noontime gas purchases. A few cents here and there do add up, often up to several hundred dollars a year.