Mercedes-Benz G550 4x4 SUV
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Mercedes-Benz G550 4x4 SUV

With vacationers facing the highest gasoline prices since 2014 this Memorial Day weekend, car shoppers may pay a lot more attention to fuel economy ratings.

Gas prices have stayed low for so long they haven't been much of a concern. But that's changed. A gallon of regular averaged $2.93 a gallon Tuesday, up from $2.76 a month ago and $2.36 a year ago, according to AAA daily survey. The prospect of $3 gas looms.

While automakers have worked to improve the gas mileage of their vehicles as they cope with tougher government standards, there will always be vehicles that lag behind others in their class. Despite the improvements, some still have dreadful gas-mileage ratings from the Environmental Protection Agency, which lists them all in an annual report.

The Bugatti Chiron, costing nearly $3 million to purchase and only 500 planned to be built, is one of the most expensive supercars in the world. It is also the most powerful, delivering 1,500 horsepower and 1,100 ft-lbs of torque, and that's factory.

Generally, the worst include some of the most expensive vehicles — often superluxury performance cars that are typically bought by people who aren't sensitive to gas prices.

The worst overall include the Mercedes-Benz G550, a military-style SUV at home in the richest neighborhoods that is nicknamed the G-Wagon. There's also one of the most expensive cars on the market, the multi-million dollar Bugatti Chiron. Both are rated at 11 miles per gallon in combined city and highway driving.

Here are all of them, listed by class:

Two seaters. Bugatti Chiron, with its 16-cylinder engine, gets 9 miles per gallon in the city and 14 mpg on the highway. Average: 11 mpg.

Minicompact cars. The worst is another supercar, Ferrari's GTC4Lusso, at 13 mpg on average.

Subcompact cars. Bentley's Continental GT convertible is rated at 14 mpg, but Chevrolet's Camaro with the 6.2-liter, eight cylinder engine isn't much better at 15 mpg.

Compact cars. The Rolls-Royce Dawn is bad at gas mileage as they come at 14 mpg. Can't afford a Rolls? The Mercedes-AMG S65 Coupe and BMW M6 Gran Coupe both get 16 mpg in combined driving.

Midsize cars.The Bentley Flying Spur and Mulsanne both get 14 mpg. So does the Rolls-Royce Wraith.

Large cars. Sure, Rolls-Royce's largest cars, the Ghost and Phantom, are at the top of the worst list at 14 mpg. But the BMW M760i xDrive isn't far behind at 16 mpg.

Small pickup trucks. You won't find any worse than the Nissan Frontier or Chevrolet Colorado ZR2, both four-wheel-drive models, at 17 mpg.

Standard pickup trucks. The Toyota Tundra with the 5.7-liter V-8 engine gets 14 mpg. Ford's F-150 Raptor is right behind at 16 mpg.

Small SUVs. Mercedes-Benz GLC63 4Matic get 18 mpg. Dodge Journey with the 3.6-liter V-6 engine, Volkswagen Atlas, Hyundai Santa Fe Ultimate and Jeep Wrangler Unlimited all get 19 mpg.

Standard SUVs. Besides the Mercedes G550 at 11 mpg, the Jeep Grand Cherokee comes in at 13 mpg.