Both texes are right. It explains alot knowing that the very purpose of the invention of diesel engines in the late 1800's was to create something better and more efficient than the gasoline engine. Diesel engines are proven to be much more efficient, both because of the design of the engine and the diesel fuel it uses (diesel fuel...or even vegetable oil for that matter... are composed of much longer hydrocarbon molecules, which contain much more potential energy. Diesel engines (even the "dirty" diesel engines as opposed to "clean diesel") burn much cleaner as well. The infamous black soot that is sometimes coughed out of the exaust is essentially pure carbon, which is completely harmless to the environment. Gas emissions are simply perceived to be cleaner because it is invisible to the naked eye. Gas emissions also emit more harmful gases to the ozone because it is less efficient in burning the fuel in the first place. Let's just face it. Diesel beats Gas any day of the week.