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The 2007 model year ushers in a new era of diesel engine technology. The previously established image of diesel engines as noisy and dirty will be radically altered as new NOx and particulate emissions standards set by the EPA go into effect.

Every diesel-powered vehicle that operates on the road will be affected. "If it has four wheels and it runs on public roads, it is going to have to have a diesel particulate filter," says Steve Matsil, vehicle chief engineer - medium-duty commercial trucks and full-size vans, General Motors.

In addition, increased use of exhaust gas recirculation (EGR) - with larger EGR coolers, closed crankcase ventilation and more complex ECUs and sensors to control regeneration of the particulate filter - means the diesel engine has become a lot more sophisticated.

But the basic fundamental advantages of the diesel engine remain. They offer a longer service life and, under certain conditions, you can see up to a 30 percent increase in fuel economy. And while gas engines often boast higher horsepower ratings, it is the torque that is important when towing heavy loads.

The choice between gas and diesel often boils down to purchase price vs. cost of ownership. Diesel engines have traditionally been more expensive than gas alternatives, and this is not likely to change. The higher operating pressures require stronger blocks; turbochargers, intercoolers and high-pressure injection systems also add to the cost. And now, there are the further costs of aftertreatment systems.