Diesel Engines are more efficient than gas engines? I tend to agree with that statement because of the complete combustion achieved through "Heat Of Compression" a Diesel Engine goes through when running it's cycle.
The "Cetane" rating is the combustion rating of Diesel while the "Octane" rating classifies gasoline, so gas needs spark while diesel when atomized at high pressure ignites with heat. The diesel engine has a much higher compression ratio which helps with ignition, complete combustion and decreases wasted energy from the diesel fuel.
Here's a some interesting articles about Diesel fueled vehicles from the U.S. Government:
Did you know that only 15% of the fuel you put in your tank is used to drive your vehicle?
I am definitely a Diesel Engine supporter and always will be! Go Diesel!