WHILE CONGRESS DEBATES

whether to send consumers $100 gasoline rebate checks or temporarily suspend the 18.4-cent federal gas tax, it's up to you to fill your tank for less. With prices topping $2.92 per gallon of regular unleaded, according to the latest figures from AAA, chances are you're fully aware of and maybe even employing tactics that will help you get better mileage. Your tires are filled to just the right amount of air pressure, you've finally removed all the junk you were hauling around in your trunk, and you've actually been trying to obey the speed limit.

But the best way to cut your gas bills is to make sure you're buying the cheapest gas around. Gas prices can vary sometimes significantly from station to station. In Chicago, you might pay as much as $3.29 per gallon or as little as $2.79. So stay informed. Keep a notebook in your car to jot down the prices at gas stations you pass. And for this to really work, you'll need to note the time and date you passed by, too. (You do want to save money, don't you?)

Here's some more advice for the truly determined:

Get Your Timing Down
There are no hard and fast rules as to which day of the week or hour of the day will yield the lowest prices, says Jason Toews, co-founder of GasBuddy.com, an online a gas-price monitoring web site. Taking good notes comes in handy. Say your closest station updates its prices late every night. If prices are on the rise, you'll know that you shouldn't wait until the next morning to fill your tank. You might also call your local gas station to find out what time of day it posts new prices.

Prices also tend to change in cycles, with one station leading and the others following suit. The length of the cycle depends on where you live. Taking notes can help you figure out which station is the leader (great for when prices fall) and which lags (for when prices are on the rise).

Figure Out Your Daily Routes
Getting gas close to home might not be your best bet. Write down where you go each day, including your commute and other regular trips. Gas prices vary by zone, so you'll generally pay more in affluent neighborhoods, downtown areas and near major roadways.

Nix Your Preconceptions
Don't count out any gas station, no matter how big or small. Discount stores like Costco and Sam's Club often have low prices ("Sometimes they sell at a loss to drive people into their stores," says Toews.) But don't assume they have the best deal. On the other end of the spectrum, independent gas stations Wicked Good Gas in Maine, Gasoline Alley in Oklahoma, and so on don't necessarily have worse deals than big-name chains.

Find the Best Gas-Monitoring Web Site for Your Area
There are numerous gas price web sites out there. Some, like GasBuddy.com and GasPriceWatch.com, rely on consumers to call in. Others, like AAA's Fuel Price Finder (see table below), get their information from credit-card transactions.

Each site has advantages and disadvantages. Your best bet is to check each to determine which has the most thorough reports for your area. If the site relies on consumer call-ins, be sure to check how often the site's listings are updated.

You might also check your local media. When gas prices are on the rise, many radio and television stations will ask drivers to call in prices, and then post the results on their web sites. WCCO-TV, which covers St. Paul and Minneapolis, lists the lowest 10 each day. WNDU-16 in South Bend, Ind., lets viewers fill out an Internet form to update prices.

Know When to Cut Your Losses
For most drivers, a savings of a few cents a gallon isn't worth driving to an out-of-the-way station, says Phil Reed, consumer advice editor for Edmunds.com. But there are exceptions, such as people driving vehicles with large gas tanks (like motor homes and campers), and those towing large objects (like trailers or boats).

Updated on May 1, 2006.