Watch where you fill up. If you regularly buy along a given route (say, to work or school), notice when the gas station gets refilled by the large tanker trucks. If you know that a station has just been filled, steer clear of it for a day or two. When the tanker dumps its thousands of gallons of gas into the containers below the station, the sediment and old gas get stirred up. This sediment and bad gas gets sucked into the cars that fill up first, and can cause a decrease in fuel efficiency, as well as wear and corrosion of the spark plugs in your vehicle.

Don't fill until the last quarter tank. If you do this, it can extend your gas because you are hauling a lighter load as the tank nears empty. This also allows you to buy gas on low-cost days. However, in cold weather, you run an increased risk of condensation in the fuel tank. And you never know when you might be in an emergency and need some gasoline in your car!

Fill the tank full. If you need to fill up, fill up all the way. The more money you try to save by adding $10 today and then $20 tomorrow will be wasted since each time you will have to travel to the station and wait for a pump. Instead, do it all at once to save time and money.

Don't top off the tank. It is wasted money and bad for the environment since the extra gas evaporates in 10 minutes of driving.

Buy gas on Wednesday. Gas prices are statistically the cheapest on Wednesdays, but this is only statistically true over a large number of days. It won't be true every week.

Buy gas three days before a holiday. Gas prices almost always go up for holidays.