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Biggest Gas Guzzlers

MPG city: 11

MPG highway: 15

The 2011 Mercedes-Benz M-Class ML63 AMG midsize SUV (pictured here) costs $400 a month to run on premium gas, and so does the Mercedes-Benz G-Class G55 AMG full-size SUV with off-roading capability, says Edmunds. The Mercedes-Benz G-Class G550 SUV with off-roading capability costs $369 per month to run on premium gas.