[Mathew Green]

Here's a simple method that works for me: Under normal circumstances, when my gas gauge gets below a certain level I buy $20 of gas. That means I buy fewer gallons on days when the price is up and more gallons when the price is down, so on average I pay less than the average price for my gas (if you see what I mean).

I also keep an eye on the advertised gas prices at the four stations I pass on my way to work. When prices are especially low I stop on the way home and fill my tank all the way up, but when they are especially high I put off buying gas and reduce my purchase to $10 in anticipation of prices dropping a few cents within a week or so.

My gas tank only holds 14 gallons and I drive less than 200 miles a week, so the dollar amounts quoted above will need to be adjusted to fit individual circumstances, but the basic principle remains the same: Spending the same number of dollars each time will get you fewer gallons when the price is high, more when it's low, resulting in a lower overall average price.