Premium Gasoline:
Using higher-octane gasoline than recommended by your vehicle’s manufacturer improves neither performance nor mileage, according to the EPA. Using the lowest suitable grade of gas minimizes the amount of crude oil necessary to fill your tank — the higher the fuel grade, the more crude oil required to make it — while also saving you money.
Diesel:
Mercedes-Benz's E320 Bluetec with a diesel engine provides roughly the same performance as its E350 gasoline counterpart; however, the diesel delivers an extra 7 mpg in city driving and 9 mpg better mileage on the highway, according to EPA tests. That 35 percent efficiency gain is typical of diesel versus gasoline engines. The problem is that diesel engines pollute more than gasoline engines. There will be more diesel vehicles available in coming years as the emissions controls required to counteract the extra pollution are implemented. There are cost variables as well: The diesel E-Class costs $1,000 more than the gasoline E-Class; plus the price of diesel fuel is constantly in flux and difficult to predict.
Ethanol:
A number of new vehicles can run on E85, a blend of 85 percent ethyl alcohol and 15 percent gasoline. These so-called “flex-fuel” vehicles capable of filling up with 100 percent ethanol, 100 percent gasoline or any mix of the two are part of a strategy to reduce imported crude oil. E85 currently costs several cents per gallon less than gasoline. The lower cost is offset by the fact that it takes an extra half gallon of E85 to match the energy content of one gallon of gasoline.
In comparing the two fuels, Car and Driver found slightly improved acceleration with E85 (attributed to its octane advantage over gasoline), but 30 percent lower mileage.
According to the Department of Energy, E85 reduces some emissions while raising others. Another issue is energy savings. Growing corn to produce the ethanol depends on fuel-burning tractors in the field and delivery trucks on the highway. The bottom line is that, at least in the near future, driving on E85 will not put much of a dent in the 9.6 million barrels of crude oil we’re importing every day.
