I was talking about mpg.

Higher compression ratio = more energy extracted from same amount of fuel. Let an engine with a 9:1 CR and an engine with a 10:1 CR, running off of the same amount of fuel, idle until there is no fuel left to be used, and the 10:1 CR engine will still be running as the lower compression engine stops.

Diesels have extremely high compression. Diesel fuel has different combustions characteristics and thermal capacities over gasoline, so it isn't as black and white as I am trying to make it seem, but a diesel's typically high compression ratio is one of the reasons I was citing for being more thermally efficient, and as such, more fuel efficient.

Have I clarified my original statement?

 

Diesels also have no throttle so there is less pumping loss. They operate at full open choke all the time. Only the fuel is varied.
In addition the fuel contains more energy than petrol. The hydrocarbon chains are longer and contain more H to combine with O2. Add the compression advantage and you start to see why they work well. They can run very lean as the fuel is injected just before ignition under pressure too. So they are not stuck at stoich mixes all the time either.

 

In a general application I'd prefer the Diesel over an Otto cycle (spark ignition) engine. For transportation purposes, diesel is superior. Its just the price of gas is far cheaper here than Europe, hence the acceptance of Diesel powerplants far eclipsing the demand here. I'd drive a diesel powered Impala all day long if we got the option.

 

Diesel is superior to gasoline. As has already been mentioned, it contains more energy than gasoline, something like 15% more energy just waiting to be released! The diesel powered Audi A8 can get 40mpg! It's a 4.2L V8 that produces 480lb/ft of torque and 326hp and does it cleaner than it's gas powered counterpart.

Oh yeah, and modern diesels are a far cry from the loud, black smoke belching diesels of the 70s and 80s. A diesel powered Audi also won last year's 24 Hours of Le Mans.

 

Yeah, but the rules were pretty stacked in it's favor.