Americans are feeling pain at the pump, with gas prices continuing to soar. To adjust to the challenges posed by the rising cost of living, consumers are putting off vehicle purchases or buying smaller cars instead of more profitable trucks and SUVs. As a result, automakers are experiencing decreased sales and profits.

One of the biggest losers: Chrysler. The company is trying to rebound from a disappointing April (sales were 23-percent below the same period last year) with its own economic stimulus plan: fixed-rate gasoline for new-car buyers. But is this really a good deal for the consumer?

Chrysler is not the first to use gasoline as an incentive, and it isn't the last, as Suzuki has stepped up to offer free gas for the summer along with zero-percent financing. Discounted or even free gas speaks to consumers' hearts and purse strings. On the surface, it may seem a pretty good deal, considering the national average is $3.61/gallon. But some Chrysler vehicles don't excel at fuel economy; Chrysler doesn't currently even offer a small hybrid or an efficient subcompact car in their fleet.

For now, let's forget about the environmental or energy independence concerns of burning more fuel. Given that (generous) assumption, is $2.99 gas enough to make up for Chrysler’s lackluster fleet fuel economy when it comes to ownership costs? As you might guess, it depends on how long you keep the vehicle:

The first three years
Given current gasoline prices of $3.61, you would need to buy a car with 21 percent better fuel economy than a Chrysler product to have equal fuel costs during the three years of discounted gas. That’s a big difference, but here are some examples (all fuel economy figures are from CR's tests, and are "overall"—mixture of city and highway driving—mpg):

Six years
But let’s say that you keep a car longer than three years. After that time’s up (whether you’ve consumed your allotted quota of discounted gas or not), you go back to paying the same fuel prices as everyone else. Here the difference lessens: you would need to buy a car with about 9.5 percent better fuel economy than the Chrysler product to equal things out.

Ten years
The difference grows to be less and less—you only need to get a vehicle that gets about 5.5 percent better fuel economy.

Of course, these percentages will differ if gas prices keep on climbing. But after the three years of cheap gas are up, you could wind up having to pay to fill up a 13 mpg Dodge Durango or 16 mpg Dodge Nitro—and you'll then be paying just what everyone else is shelling out.

Beyond that, there are a lot of extenuating circumstances:

Chrysler restricts the number of gallons of gas covered by the deal to what they expect you to consume in 12,000 miles. (That’s the average annual number of miles driven in the U.S.) To do that, they use an average mpg figure for each model. That combines all of the model versions available: big engines and small engines, two-wheel drive and four-wheel drive.

If you combine that calculation method with the disparity between CR's fuel economy testing vs. the revised 2008 EPA overall estimates, you might not get all of your fuel covered:

On the other hand, if you buy the more efficient version in a model lineup (say a four-cylinder Chrysler Sebring, when the average was calculated including V6 Sebrings), you can get more quota of free gas than you'd consume. (You can use that extra on another car that you own, assuming it takes the same fuel type.) Same goes if you drive more highway miles, where fuel economy is better. The gas deal reduces the amount of the cash-back incentives. Often the savings calculated above can make up for the difference in the incentives, but sometimes it doesn't—particularly for vehicles with big initial incentives.

Keep in mind that cash-back is money instantly off of the price of the car. It reduces the loan price, thus reducing interest payments. Plus you know you’re getting the money—you don’t have to make sure you fit the rules of the discount gas deal.

On the other hand, the gas deal requires you to pay for gas with your credit card. That's no problem if you pay off your balance each month, but otherwise you’ll be paying interest on your purchases, eating into the savings. Same goes for if you would have paid cash for fuel rather than charging it as required by the deal.

One somewhat esoteric buyer category who can really benefit from this plan—someone buying a diesel heavy-duty pickup truck. Given that diesel prices are averaging $4.15 per gallon, fixing the price at the same $2.99 as gasoline is a big difference. And the Dodge Ram 2500 diesel we tested gets the same 13 mpg fuel economy as a Chevrolet Silverado/GMC Sierra heavy-duty diesel. (Then again, the 2009 Ram truck is redesigned with notable improvements over the 2008, so you might want to wait anyway.) A diesel Grand Cherokee would also benefit, but the Dodge Sprinter van isn't included in the program.

Yes, you may save some money on gas, at least in the short term. But our owner cost data shows that, even with growing fuel costs, depreciation remains the biggest chunk of vehicle ownership costs. The competitors' vehicles listed in the chart have lower depreciation than their Chrysler counterparts, saving thousands over the life of the car and erasing the savings from the cheap gas deal. Also consider that, in general, vehicles sold with hefty discounts see more rapid depreciation than those that sell for closer to retail price. After all, it has essentially depreciated BEFORE you drove it off the lot, and it will continue to drop in value soon as it leaves the dealership. A model with better fuel economy (not to mention test scores and reliability) will likely hold its value better and be cheaper to refuel, possibly negating the benefit of the gas card.

Finally, you do more with a car than put gas in it—you drive it. You want it to be comfortable and perform well. Most of the Chrysler products listed (except the now-discontinued Pacifica) score near the bottom of our Ratings, while the competing cars listed score near the top.

It's interesting that in the same week that Chrysler announced this plan, Ford announced the widespread use of six-speed automatic transmissions to improve fuel economy. Most car companies, including Chrysler, are moving to technologies like this to improve efficiency.

Of course, Chrysler has to move its current inventory now. Discount gas is a way to promote their cars. But that doesn't mean you should be swayed by cheap(er) gas to buy a vehicle that gets so-so fuel economy, loses a lot of resale, or doesn't perform well in our Ratings. As with any car purchase, it pays to do your homework, looking at the complete purchase and ownership picture, and not be swayed by advertising.

—Tom Mutchler

For tips on saving gasoline and alternative fuels, see our fuel economy guide.