"The diesel engine is inherently efficient: Even a heavy sedan can get as much as 50 miles per gallon, while producing fewer carbon dioxide emissions per mile."

"The diesel engine is inherently efficient: Even a heavy sedan can get as much as 50 miles per gallon, while producing fewer carbon dioxide emissions per mile." There seems to be a common misconception about CO2 emissions from cars, evidenced in this statement. Burning hydrocarbons produces CO2 and water. The more burned, the more emitted. The efficiency of the engine (and vehicle in total) determines how much fuel is used while driving. More efficient = less emissions. Diesel engines are thermodynamically more efficient by virtue of their higher combustion temperature and pressure. It's this same high temp and pressure that causes nitrous and sulphur oxide pollutants to form in the exhaust gas. Hence there is a definite trade-off between high thermodynamic efficiency, and NOx pollution. Diesels are more efficient, but less clean.