IT GOES AGAINST

all conventional car rental wisdom: agreeing to fill the tank up at the rental agency may actually make

more

financial sense than going to a gas station.

Hoping to keep wallet-conscious road trippers behind the wheel, car-rental agencies are offering a series of gas discounts that allows customers to snag a tank for well below the national average of $3.94 a gallon.

Combine those upfront savings with the growing fleets of fuel-efficient rental vehicles and it may even be cheaper to rent than to drive your own gas-guzzler to the family's favorite vacation spot this summer. An owner of a 2008 Dodge Durango who makes a weeklong, 1,500-mile trip between Virginia Beach, Va., and Orlando, Fla., for example, would actually save $65 by driving a 2008 Ford Focus rented from Hertz instead. (That savings includes the $186 weekly rental fee.)

Here are the latest car rental deals:

Gas Savings

When it comes to gas promotions, Hertz's is by far the most generous. As part of an early summer promotion, many Hertz locations are offering one free tank of gas. To take advantage, rent any economy- through full-size class vehicle for at least three days, and pick it up by June 30. (Use promotion code 113120 at booking.) AAA members can even claim the deal in conjunction with their regular club discount.

Not all gas promotions are so short-lived, however. Many of the major car-rental agencies, such as Avis, Dollar Thrifty Auto and Enterprise, offer gas discounts of as much as 25 cents per gallon to renters who opt to prepay for half or a full tank of gas when they pick up their car. Enterprise, for example, sets its prices at an average 15 cents lower than other area pumps, with some branches offering even more substantial savings, says company spokesman Ned Maniscalco.

Of course, there's a catch and a couple of pitfalls. Prepaying only makes sense if you return the car on empty. There's no refund for leftover fuel. In fact, rental agencies bank on you returning the car with at least some fuel in the tank which helps them recoup the discount, says David Lytle, editorial director for Frommers.com. And don't expect to reap the benefits of low rates if you opt to buy your own fuel, then later decide to let the rental agency top off the tank. If you don't prepay, you'll not only get hit with higher per-gallon prices, but also a convenience surcharge that can double the per-gallon price. At Avis's Philadelphia location, for example, refueling costs $4 more per gallon than if you signed up for prepaid fuel.

For drivers planning to rack up the miles, prepaying for discounted gas makes a lot of financial sense. To help calculate potential savings, call the rental agency and ask for the price of a gallon of regular unleaded. Then compare it with local gas station prices that you can find on monitoring sites such as GasBuddy.com and GasPriceWatch.com.

Gas Savings
If prepaying makes sense for you, here's a sampling of what you can expect at the biggest rental agencies. (Prices are for one prepaid gallon of regular unleaded, as of May 28, 2008.)
Car Rental Agency	Philadelphia ($3.95)	Denver ($3.85)	San Francisco ($4.15)
Alamo	$3.82	$3.71	$3.93
Avis	3.90	3.75	3.98
Budget	3.93	3.86	3.97
Dollar	3.85	3.66	3.96
Enterprise	3.70	3.90	3.94
Hertz	3.72	3.79	4.11
National	3.82	3.71	3.93
Thrifty	3.85	3.66	3.96

* Data from individual agency locations. Average city prices from GasBuddy.com.

Other Promotions

If you aren't planning to drive a long distance and the gas discounts don't make sense, then consider some of the special promotions below:

Summer Rental Deals
Car-Rental Agency	Promotion Details	Expiration Date
Alamo	Save $10 on weekend rates, or $20 on weekly rates for compact- through luxury-class vehicles, SUVs, convertibles and minivans. At booking use code D60C for weekend rates; AD1336ADK for weekly.	June 30
Avis	Get 50% off weekend rates on economy- through premium-class cars at airport locations. Use promotion code G540700 at booking.	June 30
Budget	Get 50% off weekend rates on economy- through premium-class cars at airport locations. Offer good for vehicle pickup through.	June 30
Enterprise	Get 50% off weekend rates for full-size or smaller vehicles.	July 2
National	Get $30 off the price of a weekly rental for compact- through luxury-class vehicles, SUVs or minivans. Use promotion code NF1982JDD at booking.	June 30

* Data from individual rental agencies.

Also See:

• 9 Ways to Save on Gas

• More Trouble Ahead for Fliers

• 5 Ways to Negotiate a Better Deal on a Home