Both or niether.

Oil is a cocktail of different hydrocarbons which means that it will generate some diesel and some gasoline as well as other stuff. This can be forced, but that reduces efficiency. If an economy was to switch to only diesel or only gasoline there would be problems. It also depends on the type of oil: different types have differnet hydrocarbon mixes.

I did some research when buying a new car and settled on a diesel Kia Sportage which gives us approx 7l/100km in real use (approx 33mpg). The gasoline version uses approx 10l/100km.

BTW: Patricia F is not correct. Diesel generates lower emissions in cars too, depending what emissions you are measuring. A diesel car generates less CO2 than an equivalent gasoline car.

Diesel engines are more expensive to make and cost more, but they tend to last longer.

Diesel does generate more soot, but that's not a "greenhouse gas". Soot is readily flushed from the atmosphere by rain etc and is fairly inert.

Written in July 2008