The Volkswagen Eco Up! is currently more fuel-efficient than any other car powered by natural gas in the world. According to the manufacturer, the new thrifty city dasher burns only 2.9 kilograms of natural gas per 100 kilometers, and its engine produces 50 kilowatts of power.That's the equivalent of a car whose gasoline consumption is 4.4 liters per 100 kilometers. The Eco Up! costs about 2,500 euros more than a comparable gasoline car, but the low price of natural gas means it amortizes after about 40,000 kilometers.