In article >, jim beam > wrote:

>since that recent octane thread we had, i've been doing a little more
>reading around on the subject of calorific content for gasoline, and
>there really is a /huge/ reluctance by anyone [in the california market
>at least] to quote figures for the energy content of their fuel.

It is true they vary. Diesel is denser than gasoline, and thus
has about 12-13% higher energy content (and about 12-14% more GHG
production) per gallon. Thus that part of the MPG benefit is not
about efficiency, just energy density.

Ethanol has about 2/3 the volumetric energy content of gasoline.

If one uses as much as 10% ethanol, I calculate roughly a 4%
decrease in energy content overall. That's just an approximation.
I'm not sure of the exact value. And I suppose most reformulated
or oxygenated gasoline uses less, so less deviation from "pure"
gasoline (which varies in itself). So yeah, there are energy
density differences, but not huge.