(March 4, 2011) SANTA MONICA, Calif. — With gas prices surging, some consumers might think it's financially smart to go green. But according to Edmunds.com, while buying hybrid and diesel cars might help save the environment, they may not actually help you save cash.

In "Why Hybrids and Diesels Don't Always Save You Money," Edmunds.com helps consumers understand the value — or lack thereof — of choosing a green alternative to an equivalent gasoline model.

"There are several good reasons to purchase a hybrid or diesel car, but in many cases, saving money isn't one of them," says Ronald Montoya, consumer advice associate at Edmunds.com. "Now that federal tax credits have expired, car buyers may be surprised to learn how long it takes for savings at the pump to offset the additional expense of buying a hybrid or diesel car."

One of the most extreme examples of poor green value is the BMW X5 xDrive35d. Based on current gas prices for a driver averaging 15,000 miles per year, the diesel alternative to the gasoline-powered X5 is estimated to take 25.2 years before the fuel savings compensate for the higher purchase price.

Other gas-savers likely to burn your money are the Volkswagen Jetta TDI and the Nissan Altima Hybrid. Each car was estimated to take 13.8 and 10.3 years, respectively, before their fuel savings would break even with their gasoline equivalents.

"These break-even points take so long because hybrids and diesels are still pricey cars," says Montoya. "Although hybrids have been around for more than 10 years, the technology hasn't been streamlined in a way that can bring costs down. Also, the hybrid and/or diesel version of a vehicle is often positioned as the brand's high-tech model and is often loaded with more options than would normally be found in the gasoline equivalent."

Mercedes GL-Class Diesel
costs less than gas model

Edmunds.com points out that some alternative-fueled reach the break-even point much more quickly before gas savings start to show. An extreme example comes from the Mercedes Benz GL-Class Diesel which actually costs almost $1,000 less than its gasoline-powered brother while also getting better fuel economy. The Lexus HS 250h, Lincoln MKZ Hybrid and Toyota Prius Hybrid, meanwhile, each take less than one year for their costs to break even with their gasoline counterparts.

Edmunds.com stresses that as gas prices fluctuate so too does the economic logic of switching to greener vehicles. Car owners considering the financial benefits of trading in for hybrids or other gas-sipping cars are urged to check Edmunds.com's gas-guzzler calculator.

Edmunds' AutoObserver.com's Data Center also offers the estimated Monthly Fuel Costs (MFC) for every 2010 and 2011 model year vehicle based on 1,250 miles driven per month and regularly updated national fuel costs. This month, the MFC section features the midsize segment. Edmunds.com finds that the Ford Fusion Hybrid offers the lowest fuel costs per month ($108) in its class, while the Volkswagen CC VR6 offers the highest ($225).

For more details on the true values of hybrids and diesels, see "Top 10 Diesels and Hybrids with the Shortest Break-Even Periods for 2011"