If you're thinking about trading in your car for a new automobile, there are lots of things to think about that we can sometimes forget to take into account one basic choice. Do you plan on gasoline or diesel? If you think a diesel truck is like an old smoky truck you laughed at years ago, then you still haven't recognized that modern diesel vehicles are almost indistinguishable from their gas driven brethren. The diesel gas mileage you get is virtually always improved, you don't see smoke any more, and better engine designs give you more engine power and a smoother ride.

The diesel engine has been given an extreme rethink, and, with proper checks and servicing each year, will provide years of fault-free functionality, while also giving more miles for your dollar. It's interesting to note that European countries are mostly more fuel wise than the USA. Most European cars are diesel driven, not gas driven. In fuel mileage comparisons, diesel almost always beats gas.

Diesel engines have not been as popular in the US because the majority of EU-make cars would not pass US emissions requirements. Of course, by not taking to diesel engines like our European cousins, we are shedding fuel savings we could have enjoyed with diesel. And that's at a time when we're hurting from fuel shortages. Perhaps it is time for a rethink.

Advances in alternative fuels led to the creation of bio diesel fuel, which effectively fixes many of our environmental and fuel supply difficulties. Instead of using crude oil to produce this fuel, the process makes use of organic material, such as sugar cane, sugar beet and corn, to create the bio fuel.

Diesel bio fuel is made by breaking down the above vegetable food crops into short chain methyl or ethyl alcohol, then mixing the liquid with traditional diesel fuel in varying blends or grades. You can even use this alcohol fuel on its own without dramatic changes to your vehicle's motor. Buses and trucks have been successfully running on bio diesel fuel for years with no reported problems.

Diesel engines return 40% more miles per gallon than gas-powered. And though diesel may cost more at the petrol station, those diesel gallons drive you considerably further. So diesel engines can really save you dollars in the long run.

While gasoline-powered cars can rarely manage 40 mpg or more, some diesel cars, such as the diminutive Smart ForFour, manage nearly 70 mpg. The ForFour has a turbocharged 3-cylinder engine and has passed the stringent US smoke emissions laws. It is being marketed in the United States by Daimler Chrysler.

But believe it or not, the ForFour is not the all-time-champion for diesel fuel efficiency. The European-made Lupo - manufactured up until 2005 - could wring out a mind-boggling 78 miles per gallon.

The results are in, and diesel gas mileage gives more mpg than gasoline mileage. That's definite.