1] Use the Web

The days of phoning every car rental company to see who's got the best rates are a thing of the past. Point your browser to one of the many car rental booking engines on the Web (Travelocity, Expedia, Orbitz, whatever) and enter your destination and dates. It will search every car rental company in the area, saving you dozens of phone calls, and return a list of options arranged by price. It will even return the names of some local companies (especially in foreign countries) that you might not know about. If you like any of the rates you see, you can reserve the car with the click of a key on your laptop.

2] Always rent the smallest car

The smallest cars have the cheapest rates, and if the location doesn't have a subcompact when you arrive, they'll give you a free upgrade to the next smallest vehicle they have on the lot. The people who deliver cars to satellite locations (called shuttlers) don't like squeezing into subcompacts any more than you do, so they don't stock the lot with small cars unless they have to. In locations with very few cars, you will often--as a result--be given a full-size car for the price of a subcompact. And if they do have a subcompact, and you want a bigger car, you can always ask for an upgrade on the spot, but there's no reason not to try for the lower rate. This strategy surely won't work at a giant airport like Miami's, where there are hundreds of cars (and therefore dozens of subcompacts) on hand. But it will work in downtown locations and smaller airports with room for only a few cars. At the Hilo airport on the Big Island of Hawaii, this tip recently landed me a convertible for the price of a subcompact.

3] Compare rates between downtown and airport locations

Say you're arriving in St. Louis on September 10, and need a car for four days. If you rent one (a subcompact, naturally) from Budget's airport location, you'll pay $51.99 a day, or a total of $207.96. But if you rent the same car from Budget's downtown location, just a few blocks from the convention center, you'll pay $39.99 a day, or a total of $159.96. And here's the best part: You get the lower rate--a savings of $48--even if you return the car to the airport. But, you may ask, doesn't it cost something to get from the airport to downtown? Yes--all of $3. That's the price of a Metrolink ride from the airport to downtown.

4] In New York, the savings can be even greater if you're willing to take a train ride to the suburbs

Say you want to rent a car for the Fourth of July. At any of Hertz's Manhattan locations, a subcompact will cost $71.99 per day. But if you take a train to Hertz's location in North White Plains, the same car rents for $42.99. The rental lot is right next to the train station, and the ride takes no more than 50 minutes from Grand Central Station ($6.50 one-way). The savings are even greater if you keep the car for a week: $311.99 at North White Plains, compared to $409.99 in Manhattan. What's more, you still get the lower rate even if you return the car in Manhattan.

5] Check differences between weekend and weekday rates

Sometimes you can save money by keeping the car longer. At airports and other locations catering to business travelers, weekend rates are so much cheaper that it might make sense to pick up a car on a Saturday or Sunday. (At some locations, there may even be more than one rate on the same day!) For example, at the Dallas-Fort Worth Airport, National charges $55.99 a day for a rental starting on Monday, July 16. If you keep the car for three days and return it Wednesday night, you pay $167.97. But if you pick up that same car on Saturday night (July 14) and keep it for four days, you pay for two days at the weekend rate of $21.99/day and two days at the rate of $48.99/day, for a total of $141.96. Voilà! A savings of $26.01! If you pick up the car Friday night, you pay only $163.95, still $4 less than what you'd pay to pick it up on Monday morning, and you get the use of a car all weekend. In Manhattan, where car-less urbanites flee the city on weekends, the equation is just the opposite. Weekday rates are lower than weekend rates, but again, you can save money by keeping the car longer. For example, if you pick up an economy car at any of Budget's Manhattan locations on Friday, August 3 at 10 a.m. and return it Sunday, August 5 at 10 p.m., you'll pay $75.99 a day, or a total of $227.97. But if you pick up the car the night before (Thursday, August 2 at 10 p.m.) and return it at the same time, you pay only $65.99 per day, or a total of $197.97. That's a savings of $30, which will more than offset the cost of storing the car overnight in an expensive Manhattan garage if you can't find a parking spot. Why do the car rental companies do this? For the same reason restaurants have early-bird specials. They want you out before the big rush. If you take a car off their hands on Thursday night, that opens up room for one more car they can rent on Friday.

6] If you're keeping the car for four or more days, check if there's a weekly rate that might be cheaper

Weekly rates for most car rentals usually kick in on the fifth day. Most rental companies' weekly rates allow you to keep the car for five, six, or seven days with no difference in price. In many cases, the weekly rate might be cheaper than the four-day rate, and in a few cases, even cheaper than a three-day rental. Here's an example of the latter: If you pick up a subcompact car from Alamo on July 13 at the Charlotte, North Carolina, airport and keep it for three days, you'll pay $60.99 a day, or a total of $182.97. Keep it for four days and you'll pay $243.06. But keep it for five days (or pick it up a day earlier) and the weekly rate of $146.99 kicks in, a savings of nearly $100.

7] Join all the frequent renter clubs you can find--the ones operated by the major car rental companies themselves (call them and request procedures for joining)

These clubs, with names like "Gold Service" or "Emerald Club," are free to join, and usually get you a minimum of a 5 percent discount. But sometimes, preferred-renter discounts are greater and even better than what you get with AAA or AARP discounts. On a three-day rental for August 3 to 5, when everybody is trying to get out of Manhattan, my Avis Wizard number saves me 15 percent. And like frequent flyer programs, some frequent renter clubs allow you to earn points toward future free rentals. In addition to the financial incentive, frequent renter status gets you better service, beginning the minute you make your reservation.

8] Always return the car with a (mostly) full tank

You don't have to fill up right outside the airport. As long as the needle says "F," nobody can say the tank isn't full. When I worked as a shuttler for a big car rental company, we filled up the cars with gas at the airport and then delivered them to satellite locations around Boston. The gas gauges still indicated a full tank, but after as much as an hour in Boston traffic (with the A/C on full blast), the tanks were obviously somewhat less than full. That said, returning your rental car (almost) full is still the most economical option. If the gauge is not on "F" when you return the car, you'll pay a fortune in refueling charges. If you pay in advance for a full tank, you'll come out ahead only if you bring the car back empty (not something you want to chance).

9] Check your automobile and health insurance policies to avoid hefty daily insurance charges

The rental companies will try to sell you additional types of insurance, ranging from liability (sometimes called liability insurance supplement) to accident (a.k.a. personal accident insurance) to policies covering personal belongings. If you already have an auto insurance policy, decline them all. Each charge is several dollars a day, and they add up fast. If you have automobile insurance, you're probably covered for rental cars; if you have health insurance, you're covered for personal injuries regardless of how you end up in the hospital. And if you have homeowner's insurance, you may be covered if somebody steals your swimsuit from your trunk. Even if you don't have homeowner's insurance, personal effects coverage is a waste of money unless you're transporting the crown jewels in your Ford Escort.

10] Check your credit card coverage to avoid CDW charges

Then there's that painful charge for a Collision Damage Waiver (CDW) or Loss Damage Waiver, both of them lures the rental companies use to get you to pay the collision portion of the insurance on their vehicles. Unless you sign the CDW agreement, sometimes adding more than $10 a day to the price of your rental, you're responsible for damage to the car in an accident. Many states (but not all) have outlawed this liability by requiring the car companies to pay for collision insurance, so you don't have to worry. But even if you rent in a state that allows CDW charges, you can decline the hefty fee by paying for your rental with a credit card that covers you in case of collision. American Express provides this service to holders of its Gold, Platinum, and Blue Cards, as well as standard green cards, but not every Visa or MasterCard does. MBNA America is one bank that does; check with your credit card's issuing bank to see if yours does too.

John Rosenthal, a New York-based freelance writer, once worked for a major car rental company