The debate about whether gasoline-electric hybrid vehicles are more cost-effective than conventionally powered models has gone on for years. Recent declines in gas prices are now playing a role.

Vincentric LLC, which measures the overall cost of owning a vehicle, says the answer depends on your choice of hybrid. The range is vast between the most and least cost-efficient of the 31 hybrids from the 2014 model year that the firm analyzed. Over five years, Toyota Motor ’s Lexus CT 200h sedan saves an owner about $7,600 vs. the brand’s non-hybrid IS 250. Meanwhile, the Lexus GS 450h hybrid sedan costs nearly $8,200 more to own over that period than the comparable conventionally powered Lexus GS 350.

Just 10 of the 31 hybrids Vincentric evaluated are less expensive to operate than their closest gasoline-only counterparts, it found. And the fuel-savings gap between hybrids and conventional models is shrinking fast. Just two years ago, Vincentric notes, 44% of all hybrids were more cost-effective than their traditional counterparts.

The little Lexus sports hatchback costs $3,150 less than the equivalent non-hybrid Lexus IS 250 sedan, while saving a whopping $6,190 in fuel costs over five years—for a total five-year cost advantage of $7,630.

“Hybrids are losing their competitive edge due to the improved fuel economy of gas-powered combustion engines and falling fuel prices,” says David Wurster, president of the Bingham Farms, Mich.-based firm.

When all the costs of ownership are calculated, 2014 hybrids cost $1,450 more to operate over a five-year period, the firm says. The biggest factor is whether fuel savings can offset a hybrid’s price premium. For instance, Nissan Motor ’s Infiniti Q70 Hybrid sedan saves an owner nearly $5,000 in fuel expense over five years compared to the gasoline-only Q70. But the hybrid version costs $5,700 more, setting owners back $2,400.

Read the full story here: http://www.forbes.com/sites/katiekerwin/2014/11/25/hybrid-cars-that-save-you-money/