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.

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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.