Potential buyers should take caution before steering clear of any brand, however, and instead do an apples-to-apples comparison of similar products, cautioned GasBuddy's senior analyst Patrick DeHaan, who noted that brand-based costs "depend upon the manufacturer's lineup.
"Honda puts out quite a few high-mileage models," DeHaan told TheDetroitBureau.com, while, "GMC is weighted to heavy-duty models which aren't going to get as good fuel economy.
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On the whole, the industry has made major strides in mileage. A study by the University of Michigan Transportation Research Institute found that fuel economy, on the whole has climbed to record levels in recent months, and with only a rare exception continues to increase each month.
Even big pickups like the GMC Sierra are getting better mileage than ever before—though DeHaan stressed that the biggest gains are coming on passenger cars.
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At the average national price for fuel this month, the tracking service estimated the Toyota Prius cost just 7.2 cents per mile to operate. That was less than a quarter of what it would take to fuel the big Chevrolet Suburban. And for two drivers putting on 1,500 miles behind the wheel, that would add up to a difference of $310.
The new GasBuddy study did not, however, do an apples-to-apples comparison, such as pitting a midsize Toyota Camry against, say, a Ford Fusion or Nissan Altima, or a Chevrolet Silverado pickup against a Toyota Tundra or Ford F-150.
But on a brand level, the truck-focused GMC was clearly the most expensive when it came to per-mile fuel costs at 21.2 cents, followed by Cadillac at 19 cents, Mercedes-Benz at 18.6 cents, Jeep at 18.5 cents a mile and Jaguar at 18.4 cents.
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While Honda was cheapest, at 12.8 cents, Kia was close behind at 12.9 cents per mile, followed by Hyundai, Volkswagen, Mazda, Subaru, Mitsubishi and Toyota.
—By CNBC Contributor Paul A. Eisenstein. Follow him on Twitter
@DetroitBureau or at thedetroitbureau.com.