Be careful on how you interpret all these statements. In general, diesel contains longer length carbon chains (more carbon bonds) than does gasoline, therefore it has a greater energy density than gasoline. Hence a gallon of diesel has more energy than a gallon of gasoline. Hence a naive "energy efficiency" when comparing diesel to gasoline at the gallon level. But if you compare the energy content on a carbon bond basis they are almost equivalent. Both are extracted from a barrel of crude. And in general, there are more medium-length carbon chains (gasoline) in crude than the long-length carbon chains (diesel). When you compare gasoline versus diesel at the crude level, the advantage of diesel over gasoline almost disappears. Therefore both statements regarding the different motors consumption values (OP's and XXX555's) could be correct. To be fair to society and ecology, we should, more often, compare an engine's energy consumption at the crude level and not the gallon level.